diff --git a/packages/core-compat-api/src/convertLegacyPlugin.test.tsx b/packages/core-compat-api/src/convertLegacyPlugin.test.tsx
index e69de29bb2..4e17c1d61b 100644
--- a/packages/core-compat-api/src/convertLegacyPlugin.test.tsx
+++ b/packages/core-compat-api/src/convertLegacyPlugin.test.tsx
@@ -0,0 +1,91 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {
+  createPlugin as createLegacyPlugin,
+  createRouteRef as createLegacyRouteRef,
+  createExternalRouteRef as createLegacyExternalRouteRef,
+  createApiFactory,
+  createApiRef,
+} from '@backstage/core-plugin-api';
+import { convertLegacyPlugin } from './convertLegacyPlugin';
+import { PageBlueprint } from '@backstage/frontend-plugin-api';
+// eslint-disable-next-line @backstage/no-relative-monorepo-imports
+import { toInternalBackstagePlugin } from '../../frontend-plugin-api/src/wiring/createFrontendPlugin';
+
+describe('convertLegacyPlugin', () => {
+  it('should convert a plain legacy plugin to a new plugin', () => {
+    expect(
+      convertLegacyPlugin(createLegacyPlugin({ id: 'test' }), {
+        extensions: [],
+      }),
+    ).toMatchInlineSnapshot(`
+      {
+        "$$type": "@backstage/BackstagePlugin",
+        "extensions": [],
+        "externalRoutes": {},
+        "featureFlags": [],
+        "getExtension": [Function],
+        "id": "test",
+        "routes": {},
+        "toString": [Function],
+        "version": "v1",
+        "withOverrides": [Function],
+      }
+    `);
+  });
+
+  it('should convert a legacy plugin with options to a new plugin', () => {
+    const apiRef = createApiRef<string>({ id: 'plugin.test.client' });
+
+    const routeRef = createLegacyRouteRef({ id: 'test' });
+    const extRouteRef = createLegacyExternalRouteRef({ id: 'testExt' });
+
+    const converted = convertLegacyPlugin(
+      createLegacyPlugin({
+        id: 'test',
+        apis: [createApiFactory(apiRef, 'hello')],
+        routes: { test: routeRef },
+        externalRoutes: {
+          testExt: extRouteRef,
+        },
+        featureFlags: [{ name: 'test-flag' }],
+      }),
+      {
+        extensions: [
+          PageBlueprint.make({
+            params: { defaultPath: '/test', loader: async () => ({} as any) },
+          }),
+        ],
+      },
+    );
+
+    const internalConverted = toInternalBackstagePlugin(converted);
+
+    expect(internalConverted.id).toBe('test');
+    expect(internalConverted.routes).toEqual({
+      test: routeRef,
+    });
+    expect(internalConverted.externalRoutes).toEqual({
+      testExt: extRouteRef,
+    });
+    expect(internalConverted.featureFlags).toEqual([{ name: 'test-flag' }]);
+    expect(internalConverted.extensions.map(e => e.id)).toEqual([
+      'api:test/plugin.test.client',
+      'page:test',
+    ]);
+  });
+});
diff --git a/packages/core-compat-api/src/convertLegacyPlugin.ts b/packages/core-compat-api/src/convertLegacyPlugin.ts
index 05beb4e469..db8daea9cd 100644
--- a/packages/core-compat-api/src/convertLegacyPlugin.ts
+++ b/packages/core-compat-api/src/convertLegacyPlugin.ts
@@ -16,6 +16,7 @@
 
 import { BackstagePlugin as LegacyBackstagePlugin } from '@backstage/core-plugin-api';
 import {
+  ApiBlueprint,
   ExtensionDefinition,
   BackstagePlugin as NewBackstagePlugin,
   createFrontendPlugin,
@@ -27,11 +28,14 @@ export function convertLegacyPlugin(
   legacyPlugin: LegacyBackstagePlugin,
   options: { extensions: ExtensionDefinition<any, any>[] },
 ): NewBackstagePlugin {
+  const apiExtensions = Array.from(legacyPlugin.getApis()).map(factory =>
+    ApiBlueprint.make({ name: factory.api.id, params: { factory } }),
+  );
   return createFrontendPlugin({
     id: legacyPlugin.getId(),
     featureFlags: [...legacyPlugin.getFeatureFlags()],
     routes: convertLegacyRouteRefs(legacyPlugin.routes ?? {}),
     externalRoutes: convertLegacyRouteRefs(legacyPlugin.externalRoutes ?? {}),
-    extensions: options.extensions,
+    extensions: [...apiExtensions, ...options.extensions],
   });
 }