diff --git a/Code/CoreData/RKManagedObjectMappingOperation.m b/Code/CoreData/RKManagedObjectMappingOperation.m
index c9ad3385..265d98bf 100644
--- a/Code/CoreData/RKManagedObjectMappingOperation.m
+++ b/Code/CoreData/RKManagedObjectMappingOperation.m
@@ -54,7 +54,7 @@
 
     RKObjectRelationshipMapping *relationshipMapping = [self.objectMapping mappingForRelationship:relationshipName];
     RKObjectMappingDefinition *mapping = relationshipMapping.mapping;
-    NSAssert(mapping, @"Attempted to connect relationship for keyPath '%@' without a relationship mapping defined.");
+    NSAssert(mapping, @"Attempted to connect relationship for keyPath '%@' without a relationship mapping defined.", relationshipName);
     if (! [mapping isKindOfClass:[RKObjectMapping class]]) {
         RKLogWarning(@"Can only connect relationships for RKObjectMapping relationships. Found %@: Skipping...", NSStringFromClass([mapping class]));
         return;