diff --git a/packages/compiler/src/frontend/lowering/lower-modules.ts b/packages/compiler/src/frontend/lowering/lower-modules.ts
index 812581b88..562b879a2 100644
--- a/packages/compiler/src/frontend/lowering/lower-modules.ts
+++ b/packages/compiler/src/frontend/lowering/lower-modules.ts
@@ -636,7 +636,13 @@ export function collectNpmImports(lowerer: Lowerer, parts: FileParts[]): void {
       // graph: resolveImport follows its node_modules link to the loaded
       // TypeScript entry. Its internal `.js` spellings have already been
       // resolved to `.ts` by that graph.
-      if (!isRelativeSpecifier(spec) && resolveImport(lowerer.program, fp.sf, spec) !== null) {
+      const projectDep = isRelativeSpecifier(spec)
+        ? null
+        : resolveImport(lowerer.program, fp.sf, spec);
+      if (projectDep !== null) {
+        // A Node island package that tsconfig `paths` maps to its installed
+        // directory resolves to its declarations: it loads in Node.
+        if (projectDep.isDeclarationFile) collectIslandImport(lowerer, fp.sf, stmt, spec);
         continue;
       }
       const npm = resolveNpmImport(fp.sf.fileName, spec);
diff --git a/packages/compiler/src/frontend/program.ts b/packages/compiler/src/frontend/program.ts
index b7886cbec..c7ec1467b 100644
--- a/packages/compiler/src/frontend/program.ts
+++ b/packages/compiler/src/frontend/program.ts
@@ -5754,6 +5754,16 @@ function preflight7(load: LoadResult): {
           );
           continue;
         }
+        // A re-export from a Node island package that tsconfig `paths` maps
+        // to its installed directory: its declarations are no program
+        // module (the lowering reports the island boundary).
+        if (
+          projectReexport !== null &&
+          projectReexport.isDeclarationFile &&
+          !isRelativeSpecifier(fromSpec) &&
+          isFrontendIsland(packageNameOfSpecifier(fromSpec))
+        )
+          continue;
         const reDep = projectReexport;
         // `export * as ns from "./m"` re-exports the module NAMESPACE
         // object under a name: importers' `x.ns.member` reads resolve
@@ -5876,6 +5886,16 @@ function preflight7(load: LoadResult): {
       // Node's startup crash with Node's exact message; what keeps a compile
       // fence is unsupported builtin or types-only surface.
       if (isBare && npmStaticDep === null) {
+        // A Node island package that tsconfig `paths` maps to its
+        // installed directory resolves to its declarations here: it loads
+        // in Node, typed by them, like an island package resolved through
+        // node_modules (scope-B NI-4).
+        if (
+          projDep !== null &&
+          projDep.isDeclarationFile &&
+          isFrontendIsland(packageNameOfSpecifier(spec))
+        )
+          continue;
         if (projDep !== null && projDep.isDeclarationFile) {
           diags.push(
             unsupportedDiag(
diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6839-node-island-path-mapped/main.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6839-node-island-path-mapped/main.ts.json
new file mode 100644
index 000000000..8ae987602
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6839-node-island-path-mapped/main.ts.json
@@ -0,0 +1,18 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6839-node-island-path-mapped/main.ts"
+ ],
+ "diags": [
+  {
+   "code": "SC1010",
+   "message": "the 'pathkit' import (it resolves only to type declarations — there is no runtime implementation to compile) is not supported yet",
+   "loc": {
+    "file": "<repo>/tests/corpus/6839-node-island-path-mapped/main.ts",
+    "start": 234,
+    "end": 294
+   },
+   "milestone": "M4",
+   "hint": "relative imports (./file, ../dir/file), package.json-mediated project imports (#alias via the imports field, self-name references via exports), statically compiled npm packages, and the built-in fs, fs/promises, path, os, url, crypto, zlib, child_process, net, http, tls, https, http2, dgram, dns, dns/promises, util, util/types, string_decoder, querystring, readline, events, stream, stream/promises, stream/consumers, stream/web, buffer, assert, assert/strict, worker_threads, cluster, tty, async_hooks, timers, timers/promises, diagnostics_channel, perf_hooks, module, v8, and console modules (bare or node:-prefixed) and node:test (node:-prefixed only, like in Node) are supported"
+  }
+ ]
+}
diff --git a/tests/corpus/6839-node-island-path-mapped/main.ts b/tests/corpus/6839-node-island-path-mapped/main.ts
new file mode 100644
index 000000000..603392d02
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/main.ts
@@ -0,0 +1,21 @@
+// @requires-libnode
+// tsconfig `paths` maps an island package to its installed directory (a
+// monorepo pinning one copy): its import resolves to the package's
+// declarations, which type the program, and the package loads in Node.
+import { Paths, heavier, route, type Route } from "pathkit";
+
+interface Table<T extends Route> {
+  title: string;
+  rows: T[];
+}
+
+function render<T extends Route>(table: Table<T>): string {
+  return `${table.title}: ${table.rows.map((r) => r.label()).join(", ")}`;
+}
+
+const routes: Route[] = [route("/a", 1), route("/b", 3), route("/c", 2)];
+const table: Table<Route> = { title: "routes", rows: routes };
+console.log(render(table));
+const top = heavier(routes[0]!, routes[1]!);
+console.log(top.rank, top.label(), top === routes[1], routes.length);
+console.log(Paths.join("api", "v1"));
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.d.mts b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.d.mts
new file mode 100644
index 000000000..aa3c28f80
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.d.mts
@@ -0,0 +1,10 @@
+export interface Route {
+  readonly path: string;
+  readonly weight: number;
+  label(): string;
+}
+export type Weighted<T extends Route> = T & { readonly rank: number };
+export declare function route(path: string, weight: number): Route;
+export declare function heavier<T extends Route>(a: T, b: T): Weighted<T>;
+import * as Paths from "./paths.mjs";
+export { Paths };
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.mjs b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.mjs
new file mode 100644
index 000000000..e41172550
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/index.mjs
@@ -0,0 +1,13 @@
+// The loader picks its part with a computed require() specifier, which
+// scriptc does not compile natively: the package runs in a Node island.
+import { createRequire } from "node:module";
+const load = createRequire(import.meta.url);
+const { Route } = ["./route.cjs"].map((p) => load(p))[0];
+export function route(path, weight) {
+  return new Route(path, weight);
+}
+export function heavier(a, b) {
+  return Object.assign(b.weight > a.weight ? b : a, { rank: 1 });
+}
+import * as Paths from "./paths.mjs";
+export { Paths };
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.d.mts b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.d.mts
new file mode 100644
index 000000000..9d19dad8e
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.d.mts
@@ -0,0 +1 @@
+export declare function join(...parts: string[]): string;
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.mjs b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.mjs
new file mode 100644
index 000000000..e343ff3d2
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/paths.mjs
@@ -0,0 +1,3 @@
+export function join(...parts) {
+  return "/" + parts.join("/");
+}
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/route.cjs b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/route.cjs
new file mode 100644
index 000000000..0d53a5a65
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/build/route.cjs
@@ -0,0 +1,11 @@
+"use strict";
+class Route {
+  constructor(path, weight) {
+    this.path = path;
+    this.weight = weight;
+  }
+  label() {
+    return this.path + "@" + this.weight;
+  }
+}
+exports.Route = Route;
diff --git a/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/package.json b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/package.json
new file mode 100644
index 000000000..f39f36eb8
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/node_modules/pathkit/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "pathkit",
+  "version": "2.0.0",
+  "type": "module",
+  "types": "./build/index.d.mts",
+  "exports": { ".": { "import": "./build/index.mjs", "default": "./build/index.mjs" } }
+}
diff --git a/tests/corpus/6839-node-island-path-mapped/tsconfig.json b/tests/corpus/6839-node-island-path-mapped/tsconfig.json
new file mode 100644
index 000000000..aa3b6fe0b
--- /dev/null
+++ b/tests/corpus/6839-node-island-path-mapped/tsconfig.json
@@ -0,0 +1,8 @@
+{
+  "compilerOptions": {
+    "strict": true,
+    "paths": {
+      "pathkit": ["./node_modules/pathkit"]
+    }
+  }
+}
diff --git a/tests/fixtures/node-island/path-mapped-reexport.ts b/tests/fixtures/node-island/path-mapped-reexport.ts
new file mode 100644
index 000000000..7bb102298
--- /dev/null
+++ b/tests/fixtures/node-island/path-mapped-reexport.ts
@@ -0,0 +1,7 @@
+// Re-exports from an island package that tsconfig `paths` maps to its
+// installed directory: the type-only one is erased, the value one reports
+// the island boundary, and the package's declarations never compile as a
+// program module. The test builds it beside corpus 6839's pathkit package.
+export type { Route } from "pathkit";
+export { route } from "pathkit";
+console.log("loaded");
diff --git a/tests/harness/corpus-costs/6839-node-island-path-mapped/main.ts.json b/tests/harness/corpus-costs/6839-node-island-path-mapped/main.ts.json
new file mode 100644
index 000000000..f9a85c4e9
--- /dev/null
+++ b/tests/harness/corpus-costs/6839-node-island-path-mapped/main.ts.json
@@ -0,0 +1 @@
+{ "plain": 3300, "san": 30000 }
diff --git a/tests/harness/node-island.test.ts b/tests/harness/node-island.test.ts
index b6b54643b..971311d75 100644
--- a/tests/harness/node-island.test.ts
+++ b/tests/harness/node-island.test.ts
@@ -354,3 +354,22 @@ test("recursive JSON types cross into Node", async () => {
   const ir = JSON.stringify(deserializeModule(readFileSync(outPath, "utf8")));
   expect(ir).toContain("nodeIsland.callSync");
 }, 300_000);
+
+// Needs no libnode pack: the build fails before linking.
+test("re-exporting a path-mapped island package reports the island boundary", async () => {
+  const dir = join(outDir, "path-mapped-reexport");
+  rmSync(dir, { recursive: true, force: true });
+  const corpus = join(repoRoot, "tests/corpus/6839-node-island-path-mapped");
+  cpSync(join(corpus, "node_modules"), join(dir, "node_modules"), { recursive: true });
+  copyFileSync(join(corpus, "tsconfig.json"), join(dir, "tsconfig.json"));
+  copyFileSync(
+    join(repoRoot, "tests/fixtures/node-island/path-mapped-reexport.ts"),
+    join(dir, "main.ts"),
+  );
+  const result = await compile(join(dir, "main.ts"), { outPath: join(dir, "main"), outDir: dir });
+  expect(result.ok).toBe(false);
+  if (result.ok) return;
+  expect(result.diagnostics.map((d) => `${d.code} ${d.loc.file.slice(dir.length + 1)}`)).toEqual([
+    "SC8010 main.ts",
+  ]);
+}, 300_000);