diff --git a/.changeset/late-squids-feel.md b/.changeset/late-squids-feel.md
new file mode 100644
index 0000000000..b1e0c37b45
--- /dev/null
+++ b/.changeset/late-squids-feel.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-proxy-backend': minor
+---
+
+correct rewrite rule to avoid extra subpath in proxy path
diff --git a/plugins/proxy-backend/src/service/router.ts b/plugins/proxy-backend/src/service/router.ts
index e58bccd7af..d9829c477b 100644
--- a/plugins/proxy-backend/src/service/router.ts
+++ b/plugins/proxy-backend/src/service/router.ts
@@ -292,8 +292,8 @@ export async function createRouter(
     logger: options.logger,
   };
 
-  const externalUrl = await options.discovery.getExternalBaseUrl('proxy');
-  const { pathname: pathPrefix } = new URL(externalUrl);
+  const baseUrl = await options.discovery.getBaseUrl('proxy');
+  const { pathname: pathPrefix } = new URL(baseUrl);
 
   const proxyConfig: ProxyConfig = {
     ...(options.additionalEndpoints ?? {}),