diff --git a/packages/compiler/src/backend/llvm/emitter.ts b/packages/compiler/src/backend/llvm/emitter.ts
index 9e2d3524e..f20c63b1d 100644
--- a/packages/compiler/src/backend/llvm/emitter.ts
+++ b/packages/compiler/src/backend/llvm/emitter.ts
@@ -5882,6 +5882,9 @@ export class LlEmitter {
       // for stdin. They remain JavaScript objects in boolean contexts.
       case "procStream":
         return "true";
+      // A module namespace (a required builtin module object) is an object.
+      case "moduleNs":
+        return "true";
       case "array":
       case "record":
       case "object":
diff --git a/packages/compiler/src/frontend/lowering/lower-stmts.ts b/packages/compiler/src/frontend/lowering/lower-stmts.ts
index 36abb9130..4a6fb15a3 100644
--- a/packages/compiler/src/frontend/lowering/lower-stmts.ts
+++ b/packages/compiler/src/frontend/lowering/lower-stmts.ts
@@ -30,6 +30,7 @@ import {
 import {
   cjsExportMemberWriteGlobalOf,
   isCjsExportsIdentifier,
+  isCjsModuleExports,
   isFreshExportsReset,
 } from "./cjs-exports-object.js";
 import { isDeadTscHelperDecl, tscInteropBindingOfDecl } from "./cjs-tsc-interop.js";
@@ -6627,6 +6628,25 @@ export function lowerExprStatement(lowerer: Lowerer, expr: ts.Expression): IrStm
       "require() outside the module's top level (move it to the top of the file)",
     );
   }
+  // Replacing the export object (or rebinding `exports`) anywhere but a
+  // top-level statement makes the module's exports depend on which path
+  // ran (`cond ? module.exports = a : module.exports = b`, an
+  // environment-dependent branch); the static export table has one shape.
+  if (
+    !topLevelJs &&
+    isJsSourceFile(expr.getSourceFile()) &&
+    ts.isBinaryExpression(expr) &&
+    expr.operatorToken.kind === ts.SyntaxKind.EqualsToken &&
+    (isCjsModuleExports(lowerer, expr.left) || isCjsExportsIdentifier(lowerer, expr.left))
+  ) {
+    lowerer.unsupported(
+      "SC1090",
+      expr.left,
+      isCjsModuleExports(lowerer, expr.left)
+        ? "replacing module.exports outside a top-level statement (a conditional or environment-dependent export object)"
+        : "rebinding 'exports' outside a top-level statement (a conditional or environment-dependent export object)",
+    );
+  }
   if (topLevelJs && ts.isExpressionStatement(stmtNode)) {
     if (isFreshExportsReset(lowerer, stmtNode))
       return { kind: "block", body: [], loc: locOf(expr) };
diff --git a/packages/compiler/src/frontend/npm-static-bundled-chunks.test.ts b/packages/compiler/src/frontend/npm-static-bundled-chunks.test.ts
index f9463ea1e..1d8e39a73 100644
--- a/packages/compiler/src/frontend/npm-static-bundled-chunks.test.ts
+++ b/packages/compiler/src/frontend/npm-static-bundled-chunks.test.ts
@@ -274,3 +274,21 @@ export const g = import_g.g;
     degrade: expect.stringContaining("bundled CommonJS modules") as string,
   });
 });
+
+test("a chunk that only re-exports a builtin module becomes that module", () => {
+  const answer = expectSameBehavior(`${keyedHelper}var require_stream = __commonJS({
+  "lib/stream.js"(exports2, module2) {
+    module2.exports = require("stream");
+  }
+});
+var require_user = __commonJS({
+  "lib/user.js"(exports2) {
+    var Stream = require_stream();
+    exports2.same = Stream === require("stream");
+  }
+});
+console.log(typeof require_stream().PassThrough, require_user().same);
+`);
+  expect(answer.chunks.map((c) => basename(c.path))).toEqual(["index.js.require_user.cjs"]);
+  expect(answer.text).toContain('typeof require("stream").PassThrough');
+});
diff --git a/packages/compiler/src/frontend/npm-static-bundled-chunks.ts b/packages/compiler/src/frontend/npm-static-bundled-chunks.ts
index 2a3ad0b53..8a6f681a3 100644
--- a/packages/compiler/src/frontend/npm-static-bundled-chunks.ts
+++ b/packages/compiler/src/frontend/npm-static-bundled-chunks.ts
@@ -23,6 +23,7 @@
  * beside it). Anything else answers a degrade reason. */
 import * as ts from "./ts7/syntax.js";
 import { helperTokens } from "./helper-tokens.js";
+import { canonicalBuiltinModule } from "./builtin-modules.js";
 
 export interface BundledChunkSplit {
   /** The bundle with chunk declarations blanked and calls respelled. */
@@ -581,10 +582,11 @@ export function splitBundledChunks(
       return {
         degrade: `its bundled CommonJS module factory '${r.text}' is used other than as a direct call`,
       };
+    const forwarded = forwarderSpec(chunk);
     callEdits.push({
       start: call.getStart(sf),
       end: call.getEnd(),
-      text: `require(${JSON.stringify(chunk.spec)})`,
+      text: `require(${JSON.stringify(forwarded ?? chunk.spec)})`,
     });
   }
   for (const name of chunks.keys()) {
@@ -596,6 +598,11 @@ export function splitBundledChunks(
   const out: BundledChunkSplit["chunks"] = [];
   const bundleEdits: Edit[] = [...callEdits];
   for (const chunk of chunks.values()) {
+    if (forwarderSpec(chunk) !== null) {
+      // A chunk that only re-exports a builtin module is that module.
+      bundleEdits.push({ start: chunk.stmt.getStart(sf), end: chunk.stmt.getEnd(), text: "" });
+      continue;
+    }
     const result = chunkSource(
       sf,
       chunk,
@@ -656,6 +663,41 @@ export function applyEdits(source: string, from: number, to: number, edits: Edit
   return text + source.slice(at, to);
 }
 
+/** The builtin module a chunk forwards, or null: a body that is exactly
+ * `module.exports = require("<builtin>")` (readable-stream's
+ * internal/streams/stream.js). Requiring the chunk is then requiring the
+ * builtin itself (same object, and loading a builtin runs no code). */
+function forwarderSpec(chunk: Chunk): string | null {
+  const moduleParam = chunk.params[1];
+  if (moduleParam === undefined) return null;
+  const stmts = chunk.body.statements.nodes.filter(
+    (st) => !(ts.isExpressionStatement(st) && ts.isStringLiteral(st.expression)),
+  );
+  const only = stmts[0];
+  if (stmts.length !== 1 || only === undefined || !ts.isExpressionStatement(only)) return null;
+  const e = unparen(only.expression);
+  if (
+    !ts.isBinaryExpression(e) ||
+    e.operatorToken.kind !== ts.SyntaxKind.EqualsToken ||
+    !ts.isPropertyAccessExpression(e.left) ||
+    !ts.isIdentifier(e.left.expression) ||
+    e.left.expression.text !== moduleParam ||
+    e.left.name.text !== "exports"
+  )
+    return null;
+  const call = unparen(e.right);
+  if (
+    !ts.isCallExpression(call) ||
+    !ts.isIdentifier(call.expression) ||
+    call.expression.text !== "require" ||
+    call.arguments.nodes.length !== 1 ||
+    !ts.isStringLiteral(call.arguments.nodes[0]!)
+  )
+    return null;
+  const spec = (call.arguments.nodes[0] as ts.StringLiteral).text;
+  return canonicalBuiltinModule(spec) !== null ? spec : null;
+}
+
 /** How code in a factory body (a chunk or a lazy ES-module initializer)
  * observes the factory's own frame, or null: its receiver, its arguments
  * object, `super`, a meta property, or (when `returns`) a top-level
diff --git a/packages/compiler/src/frontend/npm-static-cjs-exports-alias.test.ts b/packages/compiler/src/frontend/npm-static-cjs-exports-alias.test.ts
new file mode 100644
index 000000000..c3704ea29
--- /dev/null
+++ b/packages/compiler/src/frontend/npm-static-cjs-exports-alias.test.ts
@@ -0,0 +1,81 @@
+import { spawnSync } from "node:child_process";
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterAll, expect, test } from "vitest";
+import { nodeFrontendServices } from "./services-node.js";
+
+const dirs: string[] = [];
+afterAll(() => {
+  for (const dir of dirs) rmSync(dir, { recursive: true, force: true });
+});
+
+function rewrite(source: string): string | null {
+  return nodeFrontendServices().cjsFunctionExports(source, "/pkg/index.js");
+}
+
+function run(file: string) {
+  const result = spawnSync(process.execPath, [file], { encoding: "utf8" });
+  return { status: result.status, stdout: result.stdout, stderr: result.stderr };
+}
+
+/** The rewritten module prints what the original prints. */
+function expectSameBehavior(source: string): string {
+  const result = rewrite(source);
+  expect(typeof result).toBe("string");
+  const dir = mkdtempSync(join(tmpdir(), "scriptc-cjs-function-exports-"));
+  dirs.push(dir);
+  const original = join(dir, "original.cjs");
+  const rewritten = join(dir, "rewritten.cjs");
+  writeFileSync(original, source);
+  writeFileSync(rewritten, result as string);
+  const oracle = run(original);
+  expect(oracle.status).toBe(0);
+  expect(run(rewritten)).toEqual(oracle);
+  return result as string;
+}
+
+const report = `
+console.log(typeof module.exports, module.exports === Version, Object.keys(Version).join(","));
+`;
+
+test("members of a function export object read and write the function", () => {
+  const rewritten = expectSameBehavior(`exports = module.exports = Version;
+exports.parse = parse;
+module.exports.major = (v) => parse(v)[0];
+function Version(v) { return { v }; }
+function parse(v) { return v.split(".").map(Number); }
+console.log(exports.major("2.1.0"), module.exports.parse("1.2").length);
+${report}`);
+  expect(rewritten).toContain("Version.parse = parse");
+  expect(rewritten).not.toContain("exports = module.exports");
+});
+
+test.each([
+  ["a parameter", "function inner(Version) { return exports.parse; }"],
+  ["a local", "function inner() { const Version = {}; return exports.parse; }"],
+  ["a nested function", "function inner() { function Version() {} return exports.parse; }"],
+  [
+    "a catch binding",
+    "function inner() { try { throw 0; } catch (Version) { return exports.parse; } }",
+  ],
+])("a nested binding of the function's name (%s) keeps the module as it is", (_, inner) => {
+  expect(
+    rewrite(`exports = module.exports = Version;
+exports.parse = parse;
+function Version() {}
+function parse() {}
+${inner}
+`),
+  ).toBeNull();
+});
+
+test("an `exports` shorthand property keeps its key", () => {
+  const rewritten = expectSameBehavior(`exports = module.exports = Version;
+exports.tag = "v";
+function Version() {}
+const holder = { exports };
+console.log(Object.keys(holder).join(","), holder.exports === Version, holder.exports.tag);
+${report}`);
+  expect(rewritten).toContain("{ exports: Version }");
+});
diff --git a/packages/compiler/src/frontend/npm-static-cjs-exports-alias.ts b/packages/compiler/src/frontend/npm-static-cjs-exports-alias.ts
new file mode 100644
index 000000000..dfe45b862
--- /dev/null
+++ b/packages/compiler/src/frontend/npm-static-cjs-exports-alias.ts
@@ -0,0 +1,191 @@
+/* CommonJS modules whose export object is one of their own functions:
+ *
+ *   exports = module.exports = SemVer;   // or module.exports = SemVer;
+ *   exports.parse = parse;               // or module.exports.parse = …
+ *   function SemVer(version) { … }
+ *
+ * After that statement `module.exports` (and, after the rebinding form,
+ * `exports`) IS the function, so every member read or write through them
+ * is a member of the function itself. The pass respells those accesses
+ * through the function's name, the expando form both resolvers model
+ * (members on a function declaration), and drops the `exports =`
+ * rebinding the static export protocol has no storage for.
+ *
+ * Exact only while nothing can observe the module before the statement
+ * runs and nothing replaces the export object again: the statement is a
+ * top-level statement preceded only by inert declarations, it is the
+ * file's only write of `module.exports` and `exports`, the function is a
+ * top-level declaration nothing reassigns and the file's only binding of
+ * its name, and `exports`/`module` are the CommonJS globals (never
+ * declared in the file). Other shapes answer
+ * null and keep their existing treatment. */
+import * as ts from "./ts7/syntax.js";
+import {
+  applyEdits,
+  countDeclarations,
+  declaredNames,
+  isWritten,
+  references,
+  unparen,
+  type Edit,
+} from "./npm-static-bundled-chunks.js";
+
+function isModuleExports(e: ts.Expression): e is ts.PropertyAccessExpression {
+  const x = unparen(e);
+  return (
+    ts.isPropertyAccessExpression(x) &&
+    !x.questionDotToken &&
+    ts.isIdentifier(x.expression) &&
+    x.expression.text === "module" &&
+    x.name.text === "exports"
+  );
+}
+
+/** True for a statement whose evaluation runs no code that could observe
+ * the export object: declarations and member writes (`F.prototype.m =
+ * function …`) without calls, and directives. */
+function inert(stmt: ts.Statement): boolean {
+  if (ts.isFunctionDeclaration(stmt) || ts.isEmptyStatement(stmt)) return true;
+  if (ts.isExpressionStatement(stmt) && ts.isStringLiteral(stmt.expression)) return true;
+  if (ts.isExpressionStatement(stmt)) {
+    const e = unparen(stmt.expression);
+    if (
+      !ts.isBinaryExpression(e) ||
+      e.operatorToken.kind !== ts.SyntaxKind.EqualsToken ||
+      !(ts.isPropertyAccessExpression(e.left) || ts.isElementAccessExpression(e.left))
+    )
+      return false;
+    let root: ts.Expression = e.left;
+    while (ts.isPropertyAccessExpression(root) || ts.isElementAccessExpression(root))
+      root = root.expression;
+    if (!ts.isIdentifier(root) || root.text === "module" || root.text === "exports") return false;
+  } else if (!ts.isVariableStatement(stmt)) return false;
+  let calls = false;
+  ts.walkPreorder(stmt, (n) => {
+    if (calls) return "stop";
+    if (ts.isArrowFunction(n) || ts.isFunctionExpression(n)) return "skip";
+    if (ts.isCallExpression(n) || ts.isNewExpression(n) || ts.isTaggedTemplateExpression(n))
+      calls = true;
+    return undefined;
+  });
+  return !calls;
+}
+
+export function normalizeCjsFunctionExports(sf: ts.SourceFile): string | null {
+  const source = sf.text;
+  if (!source.includes("module.exports")) return null;
+  if (!sf.fileName.endsWith(".cjs") && ts.isExternalModule(sf)) return null;
+  const declared = declaredNames(sf);
+  if (declared.has("exports") || declared.has("module")) return null;
+
+  // The whole-export statement: `[exports =] module.exports = W;`.
+  let whole: { stmt: ts.ExpressionStatement; fn: string; rebinds: boolean } | null = null;
+  const stmts = sf.statements.nodes;
+  for (let i = 0; i < stmts.length; i++) {
+    const stmt = stmts[i]!;
+    if (!ts.isExpressionStatement(stmt)) continue;
+    const top = unparen(stmt.expression);
+    if (!ts.isBinaryExpression(top) || top.operatorToken.kind !== ts.SyntaxKind.EqualsToken)
+      continue;
+    let e: ts.BinaryExpression = top;
+    let rebinds = false;
+    if (ts.isIdentifier(top.left) && top.left.text === "exports") {
+      const inner = unparen(top.right);
+      if (!ts.isBinaryExpression(inner) || inner.operatorToken.kind !== ts.SyntaxKind.EqualsToken)
+        continue;
+      rebinds = true;
+      e = inner;
+    }
+    if (!isModuleExports(e.left)) continue;
+    const value = unparen(e.right);
+    if (!ts.isIdentifier(value)) return null;
+    if (whole !== null || !stmts.slice(0, i).every(inert)) return null;
+    whole = { stmt, fn: value.text, rebinds };
+  }
+  if (whole === null) return null;
+  const fnName = whole.fn;
+  const fnDecls = stmts.filter(
+    (st) => ts.isFunctionDeclaration(st) && st.name?.text === fnName && st.body !== undefined,
+  );
+  // The respelled reads name the function from wherever they sit, so no
+  // other binding of its name (a parameter, a local, a nested function)
+  // may exist anywhere in the file.
+  if (fnDecls.length !== 1 || countDeclarations(sf, fnName) !== 1) return null;
+
+  const edits: Edit[] = [];
+  let unsafe = false;
+  const refs = references(sf);
+  for (const r of refs) {
+    if (r.text === fnName && isWritten(r)) unsafe = true;
+    if (r.text === "exports") {
+      if (isWritten(r)) {
+        // Only the whole statement's own rebinding.
+        const assign = r.parent;
+        if (
+          !whole.rebinds ||
+          assign === undefined ||
+          !ts.isBinaryExpression(assign) ||
+          assign.parent !== whole.stmt ||
+          assign.left !== r
+        )
+          unsafe = true;
+        continue;
+      }
+      // Without the rebinding, `exports` keeps the replaced object.
+      if (!whole.rebinds || r.getStart(sf) < whole.stmt.getEnd()) {
+        unsafe = true;
+        continue;
+      }
+      // `{ exports }` keeps its key: the shorthand spells out the value.
+      const shorthand =
+        r.parent !== undefined && ts.isShorthandPropertyAssignment(r.parent) && r.parent.name === r;
+      edits.push({
+        start: r.getStart(sf),
+        end: r.getEnd(),
+        text: shorthand ? `exports: ${fnName}` : fnName,
+      });
+      continue;
+    }
+    if (r.text === "module") {
+      const access = r.parent;
+      if (access === undefined || !isModuleExports(access as ts.Expression)) continue;
+      const outer = access.parent;
+      if (outer !== undefined && ts.isBinaryExpression(outer) && outer.left === access) {
+        if (
+          outer.operatorToken.kind >= ts.SyntaxKind.FirstAssignment &&
+          outer.operatorToken.kind <= ts.SyntaxKind.LastAssignment &&
+          !(
+            (outer.parent === whole.stmt && !whole.rebinds) ||
+            (whole.rebinds && outer.parent?.parent === whole.stmt)
+          )
+        )
+          unsafe = true;
+        continue;
+      }
+      // A member access through module.exports: a member of the function.
+      if (
+        outer !== undefined &&
+        (ts.isPropertyAccessExpression(outer) || ts.isElementAccessExpression(outer)) &&
+        outer.expression === access
+      ) {
+        if (access.getStart(sf) < whole.stmt.getEnd() && !insideFunction(access)) unsafe = true;
+        edits.push({ start: access.getStart(sf), end: access.getEnd(), text: fnName });
+      }
+    }
+  }
+  if (unsafe) return null;
+  if (whole.rebinds) {
+    // `exports = module.exports = W` → `module.exports = W`.
+    const e = unparen(whole.stmt.expression) as ts.BinaryExpression;
+    edits.push({ start: e.getStart(sf), end: unparen(e.right).getStart(sf), text: "" });
+  }
+  if (edits.length === 0) return null;
+  return applyEdits(source, 0, source.length, edits);
+}
+
+function insideFunction(node: ts.Node): boolean {
+  for (let p = node.parent; p !== undefined && !ts.isSourceFile(p); p = p.parent) {
+    if (ts.isFunctionLike(p)) return true;
+  }
+  return false;
+}
diff --git a/packages/compiler/src/frontend/npm-static.ts b/packages/compiler/src/frontend/npm-static.ts
index e00122238..182c5b62b 100644
--- a/packages/compiler/src/frontend/npm-static.ts
+++ b/packages/compiler/src/frontend/npm-static.ts
@@ -448,7 +448,11 @@ export function npmStaticFsShadow(services: FrontendServices): NpmStaticFsShadow
           } else if (esm !== null) {
             original = esm;
           }
-          const respelled = split !== null || esm !== null;
+          // A module exporting one of its functions reaches its members
+          // through that function.
+          const fnExports = original === null ? null : services.cjsFunctionExports(original, path);
+          if (fnExports !== null) original = fnExports;
+          const respelled = split !== null || esm !== null || fnExports !== null;
           if (original !== null) {
             const namepaths = services.jsDocNamepaths(path, original);
             const source = namepaths ?? original;
diff --git a/packages/compiler/src/frontend/services.ts b/packages/compiler/src/frontend/services.ts
index c5dcbf513..2e3d686ab 100644
--- a/packages/compiler/src/frontend/services.ts
+++ b/packages/compiler/src/frontend/services.ts
@@ -2,6 +2,7 @@ import { Ts7SourceParser, type Ts7SourceKind } from "./ts7/source-parser.js";
 import { Ts7Host, type Ts7ApiFactory, type Ts7HostOptions } from "./ts7/program-host.js";
 import { lowerEsmInitsWithParser, rewriteBundlerCjsWithParser } from "./npm-static-rewrite-host.js";
 import { isBundlerCjsCandidate } from "./npm-static-rewrite-syntax.js";
+import { normalizeCjsFunctionExports } from "./npm-static-cjs-exports-alias.js";
 import {
   mayBundleChunks,
   splitBundledChunks,
@@ -91,6 +92,13 @@ export class FrontendServices {
     if (!source.includes("__esm")) return null;
     return lowerEsmInitsWithParser(this.sourceParser(), source, path);
   }
+  /** A CommonJS module whose export object is one of its functions, with
+   * its member accesses respelled through that function (null: none). */
+  cjsFunctionExports(source: string, path: string): string | null {
+    this.ensureOpen();
+    if (!source.includes("module.exports")) return null;
+    return normalizeCjsFunctionExports(this.parse(path, source, "js"));
+  }
   nullableClassFields(path: string, source: string): syntax.NpmStaticOverloadRewrite | null {
     return syntax.applyNpmStaticNullableClassFields(this.parse(path, source, "js"), source);
   }
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/required-module-truthiness.cjs.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/required-module-truthiness.cjs.json
new file mode 100644
index 000000000..101bb2d57
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/required-module-truthiness.cjs.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/required-module-truthiness.cjs"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts.json
new file mode 100644
index 000000000..caf2144ad
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts.json
new file mode 100644
index 000000000..e255c754a
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts"
+ ],
+ "diags": []
+}
diff --git a/tests/corpus/required-module-truthiness.cjs b/tests/corpus/required-module-truthiness.cjs
new file mode 100644
index 000000000..626d1cd4d
--- /dev/null
+++ b/tests/corpus/required-module-truthiness.cjs
@@ -0,0 +1,10 @@
+// A required builtin module object in a boolean context is truthy, as any
+// object: readable-stream's `process.env.READABLE_STREAM === "disable" &&
+// Stream` and `Stream || exports` guards.
+"use strict";
+var Stream = require("stream");
+var os = require("os");
+console.log(Stream ? "stream" : "none", !!os, !os);
+console.log(process.env.SCRIPTC_UNSET_FLAG === "disable" && Stream ? "disabled" : "default");
+var fallback = Stream || null;
+console.log(fallback === Stream);
diff --git a/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts b/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts
new file mode 100644
index 000000000..29e65cbfc
--- /dev/null
+++ b/tests/fixtures/npm/cases/2583-cjs-function-exports/main.ts
@@ -0,0 +1,12 @@
+// CommonJS modules whose export object is one of their own functions:
+// semver 5/6's `exports = module.exports = Version` with members attached
+// through both `exports` and `module.exports` (and read back through
+// `exports` inside the module), and a constructor function exported whole
+// with function and value members attached afterwards.
+import Version from "gtfnexports";
+import Point from "gtfnmembers";
+
+const v = Version.parse("2.4.1");
+console.log(v === null ? "null" : v.major(), String(new Version("3.0.0")));
+console.log(Version.compare("5.0.0", "3.2.0"), Version.gt("1.0.0", "2.0.0"), Version.MAX_LENGTH);
+console.log(Point.origin().sum(), new Point(2, 3).sum(), Point.dimensions);
diff --git a/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts b/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts
new file mode 100644
index 000000000..2c117e914
--- /dev/null
+++ b/tests/fixtures/npm/cases/2584-cjs-conditional-exports/main.ts
@@ -0,0 +1,7 @@
+// An environment-dependent export object (readable-stream 2.x's
+// READABLE_STREAM=disable switch): module.exports is replaced inside an
+// if/else, so the module's exports depend on which branch ran. scriptc
+// names the construct; Node picks the branch at load.
+import rs from "gtcondexports";
+
+console.log(rs.Readable.name);
diff --git a/tests/fixtures/npm/node_modules/gtcondexports/index.d.ts b/tests/fixtures/npm/node_modules/gtcondexports/index.d.ts
new file mode 100644
index 000000000..ba94e150b
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtcondexports/index.d.ts
@@ -0,0 +1,2 @@
+declare const exported: { Readable: Function; Stream: unknown; name: string };
+export = exported;
diff --git a/tests/fixtures/npm/node_modules/gtcondexports/index.js b/tests/fixtures/npm/node_modules/gtcondexports/index.js
new file mode 100644
index 000000000..b4017d055
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtcondexports/index.js
@@ -0,0 +1,14 @@
+var Stream = require("stream");
+function Local(name) {
+  this.name = name;
+}
+if (process.env.GT_STREAMS === "native" && Stream) {
+  module.exports = Stream;
+  exports = module.exports = Stream.Readable;
+  exports.Readable = Stream.Readable;
+  exports.Stream = Stream;
+} else {
+  exports = module.exports = Local;
+  exports.Stream = Stream || exports;
+  exports.Readable = exports;
+}
diff --git a/tests/fixtures/npm/node_modules/gtcondexports/package.json b/tests/fixtures/npm/node_modules/gtcondexports/package.json
new file mode 100644
index 000000000..eab4647ed
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtcondexports/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "gtcondexports",
+  "version": "1.0.0",
+  "description": "readable-stream 2.x's environment-dependent export object: module.exports is replaced (and exports rebound) inside an if/else on an environment variable",
+  "main": "index.js",
+  "types": "index.d.ts"
+}
diff --git a/tests/fixtures/npm/node_modules/gtfnexports/index.d.ts b/tests/fixtures/npm/node_modules/gtfnexports/index.d.ts
new file mode 100644
index 000000000..c2ee082d3
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnexports/index.d.ts
@@ -0,0 +1,13 @@
+declare class Version {
+  constructor(raw: string);
+  raw: string;
+  major(): number;
+  toString(): string;
+}
+declare namespace Version {
+  const MAX_LENGTH: number;
+  function parse(raw: string): Version | null;
+  function compare(a: string, b: string): number;
+  function gt(a: string, b: string): boolean;
+}
+export = Version;
diff --git a/tests/fixtures/npm/node_modules/gtfnexports/index.js b/tests/fixtures/npm/node_modules/gtfnexports/index.js
new file mode 100644
index 000000000..d64b58f0c
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnexports/index.js
@@ -0,0 +1,25 @@
+exports = module.exports = Version;
+
+var label = process.env.GT_LABEL ? "[" + process.env.GT_LABEL + "]" : "";
+
+function Version(raw) {
+  this.raw = raw;
+  this.parts = raw.split(".");
+}
+Version.prototype.major = function () {
+  return Number(this.parts[0]);
+};
+Version.prototype.toString = function () {
+  return label + this.raw;
+};
+
+exports.MAX_LENGTH = 256;
+exports.parse = function parse(raw) {
+  return raw.length > exports.MAX_LENGTH ? null : new Version(raw);
+};
+exports.compare = function compare(a, b) {
+  return exports.parse(a).major() - exports.parse(b).major();
+};
+module.exports.gt = function gt(a, b) {
+  return exports.compare(a, b) > 0;
+};
diff --git a/tests/fixtures/npm/node_modules/gtfnexports/package.json b/tests/fixtures/npm/node_modules/gtfnexports/package.json
new file mode 100644
index 000000000..4524cd1bc
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnexports/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "gtfnexports",
+  "version": "1.0.0",
+  "description": "semver 5/6's export idiom: exports = module.exports = Version, then members attached through exports and module.exports",
+  "main": "index.js",
+  "types": "index.d.ts"
+}
diff --git a/tests/fixtures/npm/node_modules/gtfnmembers/index.d.ts b/tests/fixtures/npm/node_modules/gtfnmembers/index.d.ts
new file mode 100644
index 000000000..ea1888e0b
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnmembers/index.d.ts
@@ -0,0 +1,11 @@
+declare class Point {
+  constructor(x: number, y: number);
+  x: number;
+  y: number;
+  sum(): number;
+}
+declare namespace Point {
+  function origin(): Point;
+  const dimensions: number;
+}
+export = Point;
diff --git a/tests/fixtures/npm/node_modules/gtfnmembers/index.js b/tests/fixtures/npm/node_modules/gtfnmembers/index.js
new file mode 100644
index 000000000..6eaf003f7
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnmembers/index.js
@@ -0,0 +1,13 @@
+"use strict";
+function Point(x, y) {
+  this.x = x;
+  this.y = y;
+}
+Point.prototype.sum = function () {
+  return this.x + this.y;
+};
+module.exports = Point;
+module.exports.origin = function origin() {
+  return new Point(0, 0);
+};
+module.exports.dimensions = 2;
diff --git a/tests/fixtures/npm/node_modules/gtfnmembers/package.json b/tests/fixtures/npm/node_modules/gtfnmembers/package.json
new file mode 100644
index 000000000..5179c6caf
--- /dev/null
+++ b/tests/fixtures/npm/node_modules/gtfnmembers/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "gtfnmembers",
+  "version": "1.0.0",
+  "description": "a constructor function as module.exports with function and value members attached through module.exports afterwards",
+  "main": "index.js",
+  "types": "index.d.ts"
+}
diff --git a/tests/harness/npm-cases.ts b/tests/harness/npm-cases.ts
index ef46a59de..01718abf9 100644
--- a/tests/harness/npm-cases.ts
+++ b/tests/harness/npm-cases.ts
@@ -19,13 +19,13 @@ export function npmCases(fixturesRoot: string): NpmCase[] {
   return [
     ...globSync(join(fixturesRoot, "npm/cases/*/main.ts"))
       .sort()
-      // 2465-2469, 2556-2567, 2571 and 2580-2582 are the --npm-static bundler-emitted-CJS
+      // 2465-2469, 2556-2567, 2571 and 2580-2584 are the --npm-static bundler-emitted-CJS
       // cases (npm-static.test.ts drives them with the opt-in): their
       // consumers exercise the static rewrite's surface (lexer-visible
       // names the shipped .d.ts never declares, the __toESM interop
       // family), so they stay out of the flagless island lane by design.
       .filter(
-        (entry) => !/\/(246[5-9]|255[6-9]|256[0-7]|2571|258[0-2])-[^/]+\/main\.ts$/.test(entry),
+        (entry) => !/\/(246[5-9]|255[6-9]|256[0-7]|2571|258[0-4])-[^/]+\/main\.ts$/.test(entry),
       )
       .map((entry) => ({
         name: entry.split("/").at(-2)!,
diff --git a/tests/harness/npm-static.test.ts b/tests/harness/npm-static.test.ts
index d48f9aea2..c16567f47 100644
--- a/tests/harness/npm-static.test.ts
+++ b/tests/harness/npm-static.test.ts
@@ -76,7 +76,7 @@ async function buildStatic(entry: string, npmStatic: string[] | "auto"): Promise
     ...globSync(
       join(fixturesRoot, "npm/node_modules/cryptozoo/**/*.{js,mjs,cjs,json,d.ts}"),
     ).sort(),
-    // the bundler-emitted-CJS mini packages (cases 2465-2469, 2556-2567, 2571, 2580-2582)
+    // the bundler-emitted-CJS mini packages (cases 2465-2469, 2556-2567, 2571, 2580-2584)
     ...globSync(join(fixturesRoot, "npm/node_modules/gt*/**/*.{js,cjs,json}")).sort(),
     ...globSync(join(fixturesRoot, "npm/store/gt*/**/*.{js,cjs,json}")).sort(),
   ];
@@ -1514,6 +1514,32 @@ describe(`npm-static pilots${sanitize ? " (sanitized)" : ""}`, () => {
     expect(nativeRes.exitCode).toBe(nodeRes.exitCode);
   }, 180_000);
 
+  // 2583: a module whose export object is one of its functions (semver
+  // 5/6's `exports = module.exports = Version`), under both values of the
+  // environment variable the module reads.
+  test("function export objects 2583-cjs-function-exports compile statically and byte-match Node", async () => {
+    const entry = join(fixturesRoot, "npm/cases/2583-cjs-function-exports/main.ts");
+    await expectNodeParity(entry, ["gtfnexports", "gtfnmembers"]);
+    const binary = await buildStatic(entry, ["gtfnexports", "gtfnmembers"]);
+    const env = { ...process.env, GT_LABEL: "x" };
+    const [nodeRes, nativeRes] = await Promise.all([
+      runBinary("node", [entry], env),
+      runBinary(binary, [], env),
+    ]);
+    expect(nativeRes.stdout.toString("utf8")).toBe(nodeRes.stdout.toString("utf8"));
+    expect(nativeRes.stdout.toString("utf8")).toContain("[x]");
+  }, 180_000);
+
+  // 2584: an export object replaced inside an environment-dependent branch
+  // (readable-stream 2.x) is named precisely.
+  test("an environment-dependent export object is refused by name", () => {
+    const entry = join(fixturesRoot, "npm/cases/2584-cjs-conditional-exports/main.ts");
+    const { coverage } = analyze(entry, { npmStatic: ["gtcondexports"] });
+    expect(JSON.stringify(coverage)).toContain(
+      "replacing module.exports outside a top-level statement (a conditional or environment-dependent export object)",
+    );
+  }, 120_000);
+
   // 2567: an export that reads `this`, called through its namespace, sees
   // Node's module object; the lowered namespace would differ, so the
   // package stays refused.