diff --git a/lib/schema.js b/lib/schema.js
index f26118ca..eca1a17b 100644
--- a/lib/schema.js
+++ b/lib/schema.js
@@ -134,7 +134,9 @@ function Schema(name, settings) {
                 }
             });
         } else {
-            process.nextTick(cb);
+            if (cb) {
+                process.nextTick(cb);
+            }
         }
     };
 };