diff --git a/.changeset/fuzzy-points-whisper.md b/.changeset/fuzzy-points-whisper.md
new file mode 100644
index 0000000000..d1af2b2dcf
--- /dev/null
+++ b/.changeset/fuzzy-points-whisper.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-auth-backend': patch
+---
+
+Fixed serialization issue with caching of public keys in AWS ALB auth provider
diff --git a/plugins/auth-backend/src/providers/aws-alb/provider.ts b/plugins/auth-backend/src/providers/aws-alb/provider.ts
index a5db2869b5..61ea10947e 100644
--- a/plugins/auth-backend/src/providers/aws-alb/provider.ts
+++ b/plugins/auth-backend/src/providers/aws-alb/provider.ts
@@ -95,13 +95,13 @@ export class AwsAlbAuthProvider implements AuthProviderRouteHandlers {
   async getKey(keyId: string): Promise<KeyObject> {
     const optionalCacheKey = this.keyCache.get<KeyObject>(keyId);
     if (optionalCacheKey) {
-      return optionalCacheKey;
+      return crypto.createPublicKey(optionalCacheKey);
     }
     const keyText: string = await fetch(
       `https://public-keys.auth.elb.${this.options.region}.amazonaws.com/${keyId}`,
     ).then(response => response.text());
     const keyValue = crypto.createPublicKey(keyText);
-    this.keyCache.set(keyId, keyValue);
+    this.keyCache.set(keyId, keyValue.export({ format: 'pem', type: 'spki' }));
     return keyValue;
   }
 }