diff --git a/src/playground-project.ts b/src/playground-project.ts
index 906c86f3..901e6ce2 100644
--- a/src/playground-project.ts
+++ b/src/playground-project.ts
@@ -833,7 +833,6 @@ const fetchProjectConfig = async (
 
   return {
     ...result,
-    cdnBaseUrl: config.cdnBaseUrl,
   };
 };
 
@@ -1090,3 +1089,5 @@ const playgroundFilesDeepEqual = (
   }
   return true;
 };
+
+export { fetchProjectConfig, expandProjectConfig };
diff --git a/src/test/expanded-config_test.ts b/src/test/expanded-config_test.ts
new file mode 100644
index 00000000..9446f9e9
--- /dev/null
+++ b/src/test/expanded-config_test.ts
@@ -0,0 +1,60 @@
+import { expandProjectConfig } from '../playground-project.js';
+import { assert } from '@esm-bundle/chai';
+
+suite('expandProjectConfig cdnBaseUrl behavior', () => {
+  const originalFetch = globalThis.fetch;
+
+  setup(() => {
+    // Mock fetch to return a parent config when requested
+    globalThis.fetch = async (input: RequestInfo | URL): Promise<Response> => {
+      const url = typeof input === 'string' ? input : input.toString();
+      if (url.endsWith('parent-config.json')) {
+        return {
+          status: 200,
+          json: async () => ({
+            files: {
+              'parent.txt': { content: 'parent content' }
+            },
+            cdnBaseUrl: 'https://parent-cdn.com'
+          }),
+          text: async () => 'parent config'
+        } as Response;
+      }
+      return {
+        status: 404,
+        json: async () => ({}),
+        text: async () => 'Not Found'
+      } as Response;
+    };
+  });
+
+  teardown(() => {
+    // Restore original fetch
+    globalThis.fetch = originalFetch;
+  });
+
+  test("should use parent's cdnBaseUrl when child does not define one", async () => {
+    const childConfig = {
+      files: {
+        'child.txt': { content: 'child content' }
+      },
+      extends: 'https://example.com/parent-config.json'
+    };
+
+    const result = await expandProjectConfig(childConfig, 'https://example.com/');
+    assert.equal(result.cdnBaseUrl, 'https://parent-cdn.com');
+  });
+
+  test("should prefer child's cdnBaseUrl over parent's when defined", async () => {
+    const childConfig = {
+      files: {
+        'child.txt': { content: 'child content' }
+      },
+      cdnBaseUrl: 'https://child-cdn.com',
+      extends: 'https://example.com/parent-config.json'
+    };
+
+    const result = await expandProjectConfig(childConfig, 'https://example.com/');
+    assert.equal(result.cdnBaseUrl, 'https://child-cdn.com');
+  });
+});