diff --git a/lib/pry/commands/cat.rb b/lib/pry/commands/cat.rb
index 8889f547..47540f90 100644
--- a/lib/pry/commands/cat.rb
+++ b/lib/pry/commands/cat.rb
@@ -52,7 +52,7 @@ class Pry
       $LOAD_PATH.flat_map do |path|
         Dir[path + '/**/*'].map { |f|
           next if File.directory?(f)
-          f.sub(path + '/', '')
+          f.sub!(path + '/', '')
         }
       end
     end