diff --git a/apps/api-extractor/src/analyzer/ExportAnalyzer.ts b/apps/api-extractor/src/analyzer/ExportAnalyzer.ts
index 0bc6236aa4d..0607d63b377 100644
--- a/apps/api-extractor/src/analyzer/ExportAnalyzer.ts
+++ b/apps/api-extractor/src/analyzer/ExportAnalyzer.ts
@@ -300,6 +300,28 @@ export class ExportAnalyzer {
       return false;
     }
 
+    // If the user configured `bundledPackages` but TypeScript could not
+    // produce a `packageId` for this module, the bundled-package lookup is
+    // guaranteed to miss it and the module will be silently treated as
+    // external (issue #5730). The most common cause is a local package
+    // whose `package.json` lacks a `"version"` field — TypeScript does not
+    // assign a `packageId` without one (microsoft/TypeScript#63307). Surface
+    // the cause with a remediable error rather than producing a confusing
+    // bundling result.
+    if (packageName === undefined && this._bundledPackageNames.size > 0) {
+      throw new InternalError(
+        `Cannot determine the package name for the module ${JSON.stringify(
+          moduleSpecifier
+        )}, but "bundledPackages" is configured. ` +
+          `This is usually because the resolved package's package.json ` +
+          `is missing a "version" field — TypeScript does not assign a ` +
+          `packageId without one (microsoft/TypeScript#63307), so the ` +
+          `bundledPackages lookup cannot match it. Add a "version" field ` +
+          `(any value works) to the package's package.json and re-run.\n` +
+          SourceFileLocationFormatter.formatDeclaration(importOrExportDeclaration)
+      );
+    }
+
     if (resolvedModule.isExternalLibraryImport === undefined) {
       // This presumably means the compiler couldn't figure out whether the module was external, but we're not
       // sure how this can happen.
diff --git a/common/changes/@microsoft/api-extractor/fix-bundled-packages-missing-version_2026-05-27-19-00.json b/common/changes/@microsoft/api-extractor/fix-bundled-packages-missing-version_2026-05-27-19-00.json
new file mode 100644
index 00000000000..44d84268fae
--- /dev/null
+++ b/common/changes/@microsoft/api-extractor/fix-bundled-packages-missing-version_2026-05-27-19-00.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/api-extractor",
+      "comment": "Throw an actionable InternalError instead of silently failing to bundle when bundledPackages is configured but TypeScript could not assign a packageId to the resolved module (most often because the package's package.json is missing a \"version\" field).",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@microsoft/api-extractor"
+}
\ No newline at end of file