diff --git a/connexion/json_schema.py b/connexion/json_schema.py
index 4b1ca5885..2e7500501 100644
--- a/connexion/json_schema.py
+++ b/connexion/json_schema.py
@@ -105,7 +105,7 @@ def validate_writeOnly(validator, wo, instance, schema):
 
 Draft4ResponseValidator = extend(Draft4Validator, {
                                  'type': NullableTypeValidator,
-                                 'enum': NullableTypeValidator,
+                                 'enum': NullableEnumValidator,
                                  'required': validate_required,
                                  'writeOnly': validate_writeOnly,
                                  'x-writeOnly': validate_writeOnly})