diff --git a/pulp_deb/app/serializers/repository_serializers.py b/pulp_deb/app/serializers/repository_serializers.py
index 0f0cf98a..b8b5dccb 100644
--- a/pulp_deb/app/serializers/repository_serializers.py
+++ b/pulp_deb/app/serializers/repository_serializers.py
@@ -226,7 +226,7 @@ def check_cross_domain_config(cfg):
                 err.append(error.message)
             if err:
                 raise serializers.ValidationError(
-                    _("Provided copy criteria is invalid:'{}'".format(err))
+                    _("Provided copy criteria is invalid:'{}'").format(err)
                 )
 
             if settings.DOMAIN_ENABLED: