diff --git a/Code/Network/RKResponseMapperOperation.m b/Code/Network/RKResponseMapperOperation.m
index 5de1de906b..5a17b43cf4 100644
--- a/Code/Network/RKResponseMapperOperation.m
+++ b/Code/Network/RKResponseMapperOperation.m
@@ -386,10 +386,11 @@ - (RKMappingResult *)performMappingWithObject:(id)sourceObject error:(NSError **
                 if (objectID) {
                     if ([objectID isTemporaryID]) RKLogWarning(@"Performing object mapping to temporary target objectID. Results may not be accessible without obtaining a permanent object ID.");
                     NSManagedObject *localObject = [self.managedObjectContext existingObjectWithID:objectID error:&blockError];
-                    NSAssert([localObject.managedObjectContext isEqual:self.managedObjectContext], @"Serious Core Data error: requested existing object with ID %@ in context %@, instead got an object reference in context %@. This may indicate that the objectID for your target managed object was obtained using `obtainPermanentIDsForObjects:error:` in the wrong context.", objectID, self.managedObjectContext, [localObject managedObjectContext]);
+                    NSAssert(localObject == nil || [localObject.managedObjectContext isEqual:self.managedObjectContext], @"Serious Core Data error: requested existing object with ID %@ in context %@, instead got an object reference in context %@. This may indicate that the objectID for your target managed object was obtained using `obtainPermanentIDsForObjects:error:` in the wrong context.", objectID, self.managedObjectContext, [localObject managedObjectContext]);
                     if (! localObject) {
                         RKLogWarning(@"Failed to retrieve existing object with ID: %@", objectID);
                         RKLogCoreDataError(blockError);
+                        return;
                     }
                     self.mapperOperation.targetObject = localObject;
                 } else {