diff --git a/packages/compiler/src/frontend/npm-static-umd.test.ts b/packages/compiler/src/frontend/npm-static-umd.test.ts
new file mode 100644
index 000000000..5280ecb17
--- /dev/null
+++ b/packages/compiler/src/frontend/npm-static-umd.test.ts
@@ -0,0 +1,109 @@
+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 unwrap(source: string): string | null {
+  return nodeFrontendServices().umdFactory(source, "/pkg/index.js");
+}
+
+/** TypeScript's UMD wrapper around `body`. */
+function umd(body: string, params = "require, exports"): string {
+  return `(function (factory) {
+    if (typeof module === "object" && typeof module.exports === "object") {
+        var v = factory(require, exports);
+        if (v !== undefined) module.exports = v;
+    }
+    else if (typeof define === "function" && define.amd) {
+        define(["require", "exports"], factory);
+    }
+})(function (${params}) {
+${body}
+});
+`;
+}
+
+const probe = `
+console.log(JSON.stringify(module.exports), Object.keys(module.exports).join(","));
+`;
+
+function run(file: string): string {
+  const result = spawnSync(process.execPath, [file], { encoding: "utf8" });
+  expect(result.status).toBe(0);
+  return result.stdout;
+}
+
+/** The unwrapped module exports what the original exports. */
+function expectSameModule(source: string): string {
+  const result = unwrap(source);
+  expect(typeof result).toBe("string");
+  const dir = mkdtempSync(join(tmpdir(), "scriptc-umd-"));
+  dirs.push(dir);
+  const original = join(dir, "original.cjs");
+  const unwrapped = join(dir, "unwrapped.cjs");
+  writeFileSync(original, source + probe);
+  writeFileSync(unwrapped, result! + probe);
+  const answer = run(original);
+  expect(run(unwrapped)).toBe(answer);
+  return result!;
+}
+
+test("the factory body runs at the top level with its positions kept", () => {
+  const source = umd(`    "use strict";
+    Object.defineProperty(exports, "__esModule", { value: true });
+    exports.twice = twice;
+    const path = require("path");
+    exports.sep = path.sep;
+    function twice(n) {
+        return n * 2;
+    }`);
+  const result = expectSameModule(source);
+  expect(result.length).toBe(source.length);
+  expect(result.split("\n").length).toBe(source.split("\n").length);
+  expect(result.indexOf("exports.twice = twice;")).toBe(source.indexOf("exports.twice = twice;"));
+  expect(result).not.toContain("define.amd");
+  expect(result).not.toContain("factory");
+});
+
+test("TypeScript's helper probes of this keep their fallback", () => {
+  expectSameModule(
+    umd(`    "use strict";
+    var __importDefault = (this && this.__importDefault) || function (mod) {
+        return (mod && mod.__esModule) ? mod : { "default": mod };
+    };
+    Object.defineProperty(exports, "__esModule", { value: true });
+    const os_1 = __importDefault(require("os"));
+    exports.eol = os_1.default.EOL;`),
+  );
+});
+
+test("nested functions keep their own return, arguments and this", () => {
+  expectSameModule(
+    umd(`    "use strict";
+    exports.first = function () { return arguments[0]; };
+    exports.self = { get() { return this; } };
+    exports.arrow = () => { return 1; };`),
+  );
+});
+
+test("other shapes keep the original text", () => {
+  // `export =` returns the module value from the factory.
+  expect(unwrap(umd(`    "use strict";\n    return { a: 1 };`))).toBeNull();
+  // The body's own `this` and `arguments` differ from the module's.
+  expect(unwrap(umd(`    exports.self = this;`))).toBeNull();
+  expect(unwrap(umd(`    exports.count = arguments.length;`))).toBeNull();
+  // Other factory parameters.
+  expect(unwrap(umd(`    exports.a = 1;`, "require, exports, module"))).toBeNull();
+  expect(unwrap(umd(`    exports.a = 1;`, "req, exp"))).toBeNull();
+  // Code after the wrapper.
+  expect(unwrap(umd(`    exports.a = 1;`) + "exports.b = 2;\n")).toBeNull();
+  // Not a UMD wrapper.
+  expect(unwrap(`exports.a = 1;\n`)).toBeNull();
+});
diff --git a/packages/compiler/src/frontend/npm-static-umd.ts b/packages/compiler/src/frontend/npm-static-umd.ts
new file mode 100644
index 000000000..88400e046
--- /dev/null
+++ b/packages/compiler/src/frontend/npm-static-umd.ts
@@ -0,0 +1,178 @@
+/* TypeScript's UMD module emit in a compiled package: the module body is a
+ * factory function that the wrapper calls with the CommonJS module's own
+ * `require` and `exports`.
+ *
+ *   (function (factory) {
+ *       if (typeof module === "object" && typeof module.exports === "object") {
+ *           var v = factory(require, exports);
+ *           if (v !== undefined) module.exports = v;
+ *       }
+ *       else if (typeof define === "function" && define.amd) {
+ *           define(["require", "exports", "./dep"], factory);
+ *       }
+ *   })(function (require, exports) {
+ *       "use strict";
+ *       const dep = require("./dep");
+ *       exports.f = f;
+ *   });
+ *
+ * Under Node the CommonJS branch runs: the factory body runs once with the
+ * module's `require` and `exports`, and a body without a `return` leaves
+ * `module.exports` as it was. That is the module's own body, so the wrapper
+ * is blanked out (line breaks kept, so positions stay) and the body runs at
+ * the module's top level, where its requires and export assignments are the
+ * module's own.
+ *
+ * Accepted: the wrapper is the file's only statement, its CommonJS branch
+ * calls the factory as `factory(require, exports)`, the factory's
+ * parameters are exactly `require` and `exports`, and the body uses no
+ * `return` or `arguments` of its own. `this` in the body is the factory's
+ * receiver, not the module's: it may appear only in TypeScript's helper
+ * probes (`this && this.__importDefault`), which find no helper on either
+ * receiver. Any other shape keeps the original text. */
+import * as ts from "./ts7/syntax.js";
+import { tokenStartOfNode } from "./ts7/node-functions.js";
+import { applyEdits } from "./npm-static-bundled-chunks.js";
+
+/** True when the text may hold a UMD wrapper (a cheap probe). */
+export function mayHoldUmdWrapper(source: string): boolean {
+  return source.includes("define.amd") && source.includes("(require, exports)");
+}
+
+/** The module text with a UMD wrapper's factory body at the top level, or
+ * null when the file is not one. */
+export function unwrapUmdFactory(sf: ts.SourceFile): string | null {
+  const stmts = sf.statements.nodes;
+  if (stmts.length !== 1) return null;
+  const stmt = stmts[0]!;
+  if (!ts.isExpressionStatement(stmt) || !ts.isCallExpression(stmt.expression)) return null;
+  const call = stmt.expression;
+  if (call.arguments.nodes.length !== 1) return null;
+  const wrapper = unparenthesized(call.expression);
+  const factory = call.arguments.nodes[0]!;
+  if (!ts.isFunctionExpression(wrapper) || !ts.isFunctionExpression(factory)) return null;
+  const wrapperParams = wrapper.parameters.nodes;
+  if (wrapperParams.length !== 1 || !isPlainParameter(wrapperParams[0]!)) return null;
+  const factoryName = (wrapperParams[0]!.name as ts.Identifier).text;
+  if (!callsFactoryForCommonJs(wrapper, factoryName)) return null;
+  const params = factory.parameters.nodes;
+  if (
+    params.length !== 2 ||
+    !params.every(isPlainParameter) ||
+    (params[0]!.name as ts.Identifier).text !== "require" ||
+    (params[1]!.name as ts.Identifier).text !== "exports"
+  )
+    return null;
+  const body = factory.body;
+  if (body === undefined || !ownBodyKeepsModuleSemantics(body)) return null;
+  const open = tokenStartOfNode(body) + 1;
+  const close = body.end - 1;
+  return applyEdits(sf.text, 0, sf.text.length, [
+    { start: tokenStartOfNode(stmt), end: open, text: "" },
+    { start: close, end: stmt.end, text: "" },
+  ]);
+}
+
+function unparenthesized(e: ts.Expression): ts.Expression {
+  while (ts.isParenthesizedExpression(e)) e = e.expression;
+  return e;
+}
+
+/** A parameter that is a bare identifier: no default, rest or pattern. */
+function isPlainParameter(p: ts.ParameterDeclaration): boolean {
+  return ts.isIdentifier(p.name) && p.initializer === undefined && p.dotDotDotToken === undefined;
+}
+
+/** True when the wrapper's first statement is TypeScript's CommonJS test,
+ * `if (typeof module === "object" && typeof module.exports === "object")`,
+ * whose branch starts by calling the factory as `factory(require, exports)`. */
+function callsFactoryForCommonJs(wrapper: ts.FunctionExpression, factoryName: string): boolean {
+  const first = wrapper.body?.statements.nodes[0];
+  if (first === undefined || !ts.isIfStatement(first)) return false;
+  const sf = ts.getSourceFileOfNode(wrapper);
+  const condition = sf.text.slice(tokenStartOfNode(first.expression), first.expression.end);
+  if (
+    condition.replace(/\s+/g, " ") !==
+    'typeof module === "object" && typeof module.exports === "object"'
+  )
+    return false;
+  const branch = first.thenStatement;
+  const call = ts.isBlock(branch) ? branch.statements.nodes[0] : undefined;
+  if (call === undefined || !ts.isVariableStatement(call)) return false;
+  const declarations = call.declarationList.declarations.nodes;
+  const init = declarations.length === 1 ? declarations[0]!.initializer : undefined;
+  if (init === undefined || !ts.isCallExpression(init)) return false;
+  const args = init.arguments.nodes;
+  return (
+    ts.isIdentifier(init.expression) &&
+    init.expression.text === factoryName &&
+    args.length === 2 &&
+    ts.isIdentifier(args[0]!) &&
+    args[0].text === "require" &&
+    ts.isIdentifier(args[1]!) &&
+    args[1].text === "exports"
+  );
+}
+
+/** True when the factory body behaves the same as the module's top level:
+ * no `return` or `arguments` of its own, and `this` only in TypeScript's
+ * helper probes. */
+function ownBodyKeepsModuleSemantics(body: ts.Block): boolean {
+  let keeps = true;
+  ts.walkPreorder(body, (n) => {
+    if (!keeps) return "stop";
+    // Nested functions have their own `return`, `arguments` and `this`;
+    // arrow functions only their own `return`.
+    if (
+      ts.isFunctionDeclaration(n) ||
+      ts.isFunctionExpression(n) ||
+      ts.isMethodDeclaration(n) ||
+      ts.isGetAccessorDeclaration(n) ||
+      ts.isSetAccessorDeclaration(n) ||
+      ts.isConstructorDeclaration(n)
+    )
+      return "skip";
+    if (ts.isClassDeclaration(n) || ts.isClassExpression(n)) return "skip";
+    if (ts.isReturnStatement(n) && !insideArrow(n, body)) keeps = false;
+    else if (ts.isIdentifier(n) && n.text === "arguments") keeps = false;
+    else if (n.kind === ts.SyntaxKind.ThisKeyword && !isHelperProbe(n)) keeps = false;
+    return undefined;
+  });
+  return keeps;
+}
+
+/** True when `node` sits inside an arrow function nested in `body`. */
+function insideArrow(node: ts.Node, body: ts.Block): boolean {
+  for (let p = node.parent; p !== undefined && p !== body; p = p.parent)
+    if (ts.isArrowFunction(p)) return true;
+  return false;
+}
+
+/** `this` in TypeScript's helper probe `this && this.__name`: the left
+ * operand, or the receiver of the right operand's `__` member. */
+function isHelperProbe(node: ts.Node): boolean {
+  const parent = node.parent;
+  if (parent === undefined) return false;
+  const probe =
+    ts.isBinaryExpression(parent) && parent.left === node
+      ? parent
+      : ts.isPropertyAccessExpression(parent) &&
+          parent.expression === node &&
+          ts.isIdentifier(parent.name) &&
+          parent.name.text.startsWith("__") &&
+          parent.parent !== undefined &&
+          ts.isBinaryExpression(parent.parent) &&
+          parent.parent.right === parent
+        ? parent.parent
+        : undefined;
+  if (probe === undefined || probe.operatorToken.kind !== ts.SyntaxKind.AmpersandAmpersandToken)
+    return false;
+  const right = probe.right;
+  return (
+    probe.left.kind === ts.SyntaxKind.ThisKeyword &&
+    ts.isPropertyAccessExpression(right) &&
+    right.expression.kind === ts.SyntaxKind.ThisKeyword &&
+    ts.isIdentifier(right.name) &&
+    right.name.text.startsWith("__")
+  );
+}
diff --git a/packages/compiler/src/frontend/npm-static.ts b/packages/compiler/src/frontend/npm-static.ts
index bc9fc2abd..56edafc48 100644
--- a/packages/compiler/src/frontend/npm-static.ts
+++ b/packages/compiler/src/frontend/npm-static.ts
@@ -452,6 +452,10 @@ export function npmStaticFsShadow(services: FrontendServices): NpmStaticFsShadow
           } else if (esm !== null) {
             original = esm;
           }
+          // TypeScript's UMD wrapper calls its factory with the module's own
+          // require and exports: the factory body is the module body.
+          const umd = original === null ? null : services.umdFactory(original, path);
+          if (umd !== null) original = umd;
           // Polyfill packages that ARE a Node builtin compile as the builtin.
           const aliased = original === null ? null : services.builtinAliasRequires(original, path);
           if (aliased !== null) original = aliased;
@@ -472,6 +476,7 @@ export function npmStaticFsShadow(services: FrontendServices): NpmStaticFsShadow
           if (exportsVar !== null) original = exportsVar;
           const respelled =
             split !== null ||
+            umd !== null ||
             tscHelpers !== null ||
             esm !== null ||
             aliased !== null ||
diff --git a/packages/compiler/src/frontend/services.ts b/packages/compiler/src/frontend/services.ts
index 10931ab29..19728d6ce 100644
--- a/packages/compiler/src/frontend/services.ts
+++ b/packages/compiler/src/frontend/services.ts
@@ -12,6 +12,7 @@ import {
   mayRequireBuiltinAlias,
   rewriteBuiltinAliasRequires,
 } from "./npm-static-builtin-aliases.js";
+import { mayHoldUmdWrapper, unwrapUmdFactory } from "./npm-static-umd.js";
 import { mayHoldEnumIife, rewriteEnumIifes } from "./npm-static-enum-iife.js";
 import { mayHoldTscBuiltinImport, unwrapTscBuiltinImports } from "./npm-static-tsc-helpers.js";
 import { builtinPackageAliasFor } from "./package-shims.js";
@@ -114,6 +115,13 @@ export class FrontendServices {
     if (!mayHoldTscBuiltinImport(source)) return null;
     return unwrapTscBuiltinImports(this.parse(path, source, "js"));
   }
+  /** A package module written as TypeScript's UMD wrapper with its
+   * factory body at the top level (null: not one). */
+  umdFactory(source: string, path: string): string | null {
+    this.ensureOpen();
+    if (!mayHoldUmdWrapper(source)) return null;
+    return unwrapUmdFactory(this.parse(path, source, "js"));
+  }
   /** A package module with its literal-valued TypeScript enum IIFEs
    * respelled as object literals (null: none). */
   enumIifes(source: string, path: string): string | null {
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7000-umd-package-entry/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7000-umd-package-entry/main.ts.json
new file mode 100644
index 000000000..0c6cbd9d1
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7000-umd-package-entry/main.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/7000-umd-package-entry/main.ts"
+ ],
+ "diags": []
+}
diff --git a/tests/corpus/7000-umd-package-entry/main.ts b/tests/corpus/7000-umd-package-entry/main.ts
new file mode 100644
index 000000000..4b8b3e246
--- /dev/null
+++ b/tests/corpus/7000-umd-package-entry/main.ts
@@ -0,0 +1,10 @@
+// A package whose main entry is TypeScript's UMD emit: each module's body is
+// a factory the wrapper calls with the module's own require and exports, so
+// its requires and export assignments sit inside a function. Node runs the
+// CommonJS branch, and the named imports read the factory's exports.
+import { Shape, area, describe, label, unitCount } from "umd-shapes";
+
+console.log(label, unitCount);
+console.log(area({ kind: Shape.Square, size: 3 }), area({ kind: Shape.Circle, size: 1 }).toFixed(4));
+console.log(describe({ kind: Shape.Square, size: 2 }));
+console.log(Shape.Circle, Shape[Shape.Square]);
diff --git a/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/impl/measure.js b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/impl/measure.js
new file mode 100644
index 000000000..0ea89b34e
--- /dev/null
+++ b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/impl/measure.js
@@ -0,0 +1,22 @@
+(function (factory) {
+    if (typeof module === "object" && typeof module.exports === "object") {
+        var v = factory(require, exports);
+        if (v !== undefined) module.exports = v;
+    }
+    else if (typeof define === "function" && define.amd) {
+        define(["require", "exports"], factory);
+    }
+})(function (require, exports) {
+    "use strict";
+    Object.defineProperty(exports, "__esModule", { value: true });
+    exports.units = void 0;
+    exports.square = square;
+    exports.circle = circle;
+    exports.units = ["cm", "m"];
+    function square(size) {
+        return size * size;
+    }
+    function circle(radius) {
+        return Math.PI * radius * radius;
+    }
+});
diff --git a/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.d.ts b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.d.ts
new file mode 100644
index 000000000..0982da9ef
--- /dev/null
+++ b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.d.ts
@@ -0,0 +1,12 @@
+export declare enum Shape {
+    Square = 0,
+    Circle = 1
+}
+export interface Figure {
+    kind: Shape;
+    size: number;
+}
+export declare const label: string;
+export declare const unitCount: number;
+export declare function area(figure: Figure): number;
+export declare function describe(figure: Figure): string;
diff --git a/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.js b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.js
new file mode 100644
index 000000000..26162fbd9
--- /dev/null
+++ b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/lib/main.js
@@ -0,0 +1,29 @@
+(function (factory) {
+    if (typeof module === "object" && typeof module.exports === "object") {
+        var v = factory(require, exports);
+        if (v !== undefined) module.exports = v;
+    }
+    else if (typeof define === "function" && define.amd) {
+        define(["require", "exports", "./impl/measure"], factory);
+    }
+})(function (require, exports) {
+    "use strict";
+    Object.defineProperty(exports, "__esModule", { value: true });
+    exports.unitCount = exports.label = exports.Shape = void 0;
+    exports.area = area;
+    exports.describe = describe;
+    const measure = require("./impl/measure");
+    var Shape;
+    (function (Shape) {
+        Shape[Shape["Square"] = 0] = "Square";
+        Shape[Shape["Circle"] = 1] = "Circle";
+    })(Shape || (exports.Shape = Shape = {}));
+    exports.label = "shapes";
+    exports.unitCount = measure.units.length;
+    function area(figure) {
+        return figure.kind === Shape.Square ? measure.square(figure.size) : measure.circle(figure.size);
+    }
+    function describe(figure) {
+        return `${Shape[figure.kind]} of ${figure.size} ${measure.units[0]}: ${area(figure)}`;
+    }
+});
diff --git a/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/package.json b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/package.json
new file mode 100644
index 000000000..e827ecc41
--- /dev/null
+++ b/tests/corpus/7000-umd-package-entry/node_modules/umd-shapes/package.json
@@ -0,0 +1 @@
+{ "name": "umd-shapes", "version": "1.0.0", "main": "./lib/main.js", "types": "./lib/main.d.ts" }
diff --git a/tests/harness/corpus-costs/7000-umd-package-entry/main.ts.json b/tests/harness/corpus-costs/7000-umd-package-entry/main.ts.json
new file mode 100644
index 000000000..782707a3a
--- /dev/null
+++ b/tests/harness/corpus-costs/7000-umd-package-entry/main.ts.json
@@ -0,0 +1 @@
+{ "plain": 3911, "san": 3835 }