diff --git a/lib/workers/repository/process/lookup/current.ts b/lib/workers/repository/process/lookup/current.ts
index dad2de7908c7f8dc205b970cc5276351431e4ce7..83ff6103318f9f6def958761e47856fd35ce3f04 100644
--- a/lib/workers/repository/process/lookup/current.ts
+++ b/lib/workers/repository/process/lookup/current.ts
@@ -1,3 +1,4 @@
+import is from '@sindresorhus/is';
 import { logger } from '../../../../logger';
 import type { VersioningApi } from '../../../../versioning/types';
 import type { LookupUpdateConfig } from './types';
@@ -10,6 +11,10 @@ export function getCurrentVersion(
   allVersions: string[]
 ): string | null {
   const { currentValue, lockedVersion } = config;
+  // istanbul ignore if
+  if (!is.string(currentValue)) {
+    return null;
+  }
   if (versioning.isVersion(currentValue)) {
     return currentValue;
   }