diff --git a/lib/grape/middleware/formatter.rb b/lib/grape/middleware/formatter.rb
index 858479976..d41b39e94 100644
--- a/lib/grape/middleware/formatter.rb
+++ b/lib/grape/middleware/formatter.rb
@@ -42,10 +42,10 @@ def before
 
       def format_from_extension
         parts = request.path.split('.')
-        extension = parts.last.to_sym
 
-        if parts.size > 1 && content_types.key?(extension)
-          return extension
+        if parts.size > 1
+          extension = parts.last.to_sym
+          return extension if content_types.key?(extension)
         end
         nil
       end