diff --git a/lib/grape-active_model_serializers/formatter.rb b/lib/grape-active_model_serializers/formatter.rb
index e026f1e..a6247cc 100644
--- a/lib/grape-active_model_serializers/formatter.rb
+++ b/lib/grape-active_model_serializers/formatter.rb
@@ -35,7 +35,7 @@ module Grape
           if innermost_scope[:namespace]
             innermost_scope[:namespace].space
           else
-            endpoint.options[:path][0].split('/')[-1]
+            endpoint.options[:path][0].to_s.split('/')[-1]
           end
         end
       end