diff --git a/lib/validatable.js b/lib/validatable.js
index 559b377e..2f09696e 100644
--- a/lib/validatable.js
+++ b/lib/validatable.js
@@ -143,11 +143,13 @@ Validatable.prototype.isValid = function (callback) {
     if (!async) {
         if (valid) cleanErrors(this);
         if (callback) callback(valid);
+        return valid;
+    } else {
+        // in case of async validation we should return undefined here,
+        // because not all validations are finished yet
+        return;
     }
-    
-    
 
-    return valid;
 };
 
 function cleanErrors(inst) {