diff --git a/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSource.java b/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSource.java
index de85b4aad4..8a4c476443 100644
--- a/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSource.java
+++ b/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/event/source/ExternalResourceCachingEventSource.java
@@ -78,7 +78,9 @@ protected ExternalResourceCachingEventSource(
     if (resourceIDMapper == ResourceIDMapper.resourceIdProviderMapper()
         && !ResourceIDProvider.class.isAssignableFrom(resourceClass)) {
       throw new IllegalArgumentException(
-          "resource class is not a " + ResourceIDProvider.class.getSimpleName());
+          resourceClass.getName()
+              + " is not a subclass of "
+              + ResourceIDProvider.class.getSimpleName());
     }
     this.resourceIDMapper = resourceIDMapper;
   }