diff --git a/.changeset/sixty-llamas-change.md b/.changeset/sixty-llamas-change.md
new file mode 100644
index 0000000000..a0d183d45c
--- /dev/null
+++ b/.changeset/sixty-llamas-change.md
@@ -0,0 +1,7 @@
+---
+'@backstage/plugin-catalog-backend': patch
+'@backstage/plugin-jenkins-backend': patch
+'@backstage/plugin-search-backend': patch
+---
+
+Fixed issue in `PermissionEvaluator` instance check that would cause unexpected "invalid union" errors.
diff --git a/plugins/catalog-backend/src/service/CatalogBuilder.ts b/plugins/catalog-backend/src/service/CatalogBuilder.ts
index f5f00cd0fc..57508615ac 100644
--- a/plugins/catalog-backend/src/service/CatalogBuilder.ts
+++ b/plugins/catalog-backend/src/service/CatalogBuilder.ts
@@ -382,7 +382,7 @@ export class CatalogBuilder {
     const unauthorizedEntitiesCatalog = new DefaultEntitiesCatalog(dbClient);
 
     let permissionEvaluator: PermissionEvaluator;
-    if ('query' in permissions) {
+    if ('authorizeConditional' in permissions) {
       permissionEvaluator = permissions as PermissionEvaluator;
     } else {
       logger.warn(
diff --git a/plugins/jenkins-backend/src/service/router.ts b/plugins/jenkins-backend/src/service/router.ts
index f6bd21c633..fa357f8e9f 100644
--- a/plugins/jenkins-backend/src/service/router.ts
+++ b/plugins/jenkins-backend/src/service/router.ts
@@ -40,7 +40,7 @@ export async function createRouter(
   const { jenkinsInfoProvider, permissions, logger } = options;
 
   let permissionEvaluator: PermissionEvaluator | undefined;
-  if (permissions && 'query' in permissions) {
+  if (permissions && 'authorizeConditional' in permissions) {
     permissionEvaluator = permissions as PermissionEvaluator;
   } else {
     logger.warn(
diff --git a/plugins/search-backend/src/service/router.ts b/plugins/search-backend/src/service/router.ts
index 11f0eb22e6..e42a31981c 100644
--- a/plugins/search-backend/src/service/router.ts
+++ b/plugins/search-backend/src/service/router.ts
@@ -76,7 +76,7 @@ export async function createRouter(
   });
 
   let permissionEvaluator: PermissionEvaluator;
-  if ('query' in permissions) {
+  if ('authorizeConditional' in permissions) {
     permissionEvaluator = permissions as PermissionEvaluator;
   } else {
     logger.warn(