diff --git a/activesupport/lib/active_support/core_ext/hash/keys.rb b/activesupport/lib/active_support/core_ext/hash/keys.rb
index e4d429fc2b..045a6944fa 100644
--- a/activesupport/lib/active_support/core_ext/hash/keys.rb
+++ b/activesupport/lib/active_support/core_ext/hash/keys.rb
@@ -22,7 +22,7 @@ class Hash
   # to +to_sym+.
   def symbolize_keys!
     keys.each do |key|
-      self[(key.to_sym rescue key)] = delete(key) if key.respond_to?(:to_sym) && !key.is_a?(Fixnum)
+      self[(key.to_sym rescue key) || key] = delete(key)
     end
     self
   end