diff --git a/module_build_service/web/views.py b/module_build_service/web/views.py
index 30a66f06..0af2d2c5 100644
--- a/module_build_service/web/views.py
+++ b/module_build_service/web/views.py
@@ -378,6 +378,7 @@ class BaseHandler(object):
         "require_overrides",
         "scmurl",
         "scratch",
+        "side_tag",
         "srpms",
     }
 
@@ -428,7 +429,7 @@ class BaseHandler(object):
         forbidden_params = [k for k in self.data if k not in self.valid_params]
         if forbidden_params:
             raise ValidationError(
-                "The request contains unspecified parameters: {}".format(
+                "The request contains invalid parameters: {}".format(
                     ", ".join(forbidden_params))
             )