1 files changed, 9 insertions, 3 deletions
diff --git a/activesupport/lib/active_support/core_ext/object/deep_dup.rb b/activesupport/lib/active_support/core_ext/object/deep_dup.rb
index ad5b2af161..8dfeed0066 100644
--- a/activesupport/lib/active_support/core_ext/object/deep_dup.rb
+++ b/activesupport/lib/active_support/core_ext/object/deep_dup.rb
@@ -39,9 +39,15 @@ class Hash
   #   hash[:a][:c] # => nil
   #   dup[:a][:c]  # => "c"
   def deep_dup
-    each_with_object(dup) do |(key, value), hash|
-      hash.delete(key)
-      hash[key.deep_dup] = value.deep_dup
+    hash = dup
+    each_pair do |key, value|
+      if key.frozen? && ::String === key
+        hash[key] = value.deep_dup
+      else
+        hash.delete(key)
+        hash[key.deep_dup] = value.deep_dup
+      end
     end
+    hash
   end
 end