diff --git a/connexion/api.py b/connexion/api.py
index 61e736625..e15d2de9f 100644
--- a/connexion/api.py
+++ b/connexion/api.py
@@ -88,9 +88,10 @@ def __init__(self, swagger_yaml_path, base_url=None, arguments=None,
 
         logger.debug('Read specification', extra=self.specification)
 
+        self.specification = compatibility_layer(self.specification)
         # Avoid validator having ability to modify specification
         spec = copy.deepcopy(self.specification)
-        validate_spec(compatibility_layer(spec))
+        validate_spec(spec)
 
         # https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#fixed-fields
         # If base_url is not on provided then we try to read it from the swagger.yaml or use / by default