diff --git a/.changeset/cyan-suns-shave.md b/.changeset/cyan-suns-shave.md
new file mode 100644
index 0000000000..09e51d9548
--- /dev/null
+++ b/.changeset/cyan-suns-shave.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend-module-unprocessed': patch
+---
+
+Correctly convert owner to string in case owner has not been provided
diff --git a/plugins/catalog-backend-module-unprocessed/src/UnprocessedEntitiesModule.ts b/plugins/catalog-backend-module-unprocessed/src/UnprocessedEntitiesModule.ts
index 23042ff2d8..c46848f201 100644
--- a/plugins/catalog-backend-module-unprocessed/src/UnprocessedEntitiesModule.ts
+++ b/plugins/catalog-backend-module-unprocessed/src/UnprocessedEntitiesModule.ts
@@ -162,7 +162,7 @@ export class UnprocessedEntitiesModule {
         return res.json(
           await this.unprocessed({
             reason: 'failed',
-            owner: String(req.query.owner),
+            owner: req.query.owner?.toString(),
           }),
         );
       })
@@ -170,7 +170,7 @@ export class UnprocessedEntitiesModule {
         return res.json(
           await this.unprocessed({
             reason: 'pending',
-            owner: String(req.query.owner),
+            owner: req.query.owner?.toString(),
           }),
         );
       })