diff --git a/.changeset/dry-dolls-run.md b/.changeset/dry-dolls-run.md
new file mode 100644
index 0000000000..423d14d044
--- /dev/null
+++ b/.changeset/dry-dolls-run.md
@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Use consistent file extensions for JS output when building packages.
diff --git a/packages/cli/src/lib/builder/config.ts b/packages/cli/src/lib/builder/config.ts
index 2e7847fdb1..a236e87806 100644
--- a/packages/cli/src/lib/builder/config.ts
+++ b/packages/cli/src/lib/builder/config.ts
@@ -62,7 +62,7 @@ export const makeConfigs = async (
       output.push({
         dir: 'dist',
         entryFileNames: 'index.cjs.js',
-        chunkFileNames: 'cjs/[name]-[hash].js',
+        chunkFileNames: 'cjs/[name]-[hash].cjs.js',
         format: 'commonjs',
         sourcemap: true,
       });
@@ -71,7 +71,7 @@ export const makeConfigs = async (
       output.push({
         dir: 'dist',
         entryFileNames: 'index.esm.js',
-        chunkFileNames: 'esm/[name]-[hash].js',
+        chunkFileNames: 'esm/[name]-[hash].esm.js',
         format: 'module',
         sourcemap: true,
       });