diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index f2d9df6d13..6c0cae71ed 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -315,7 +315,7 @@ module ActiveSupport
         @config = {
           :terminator => "false",
           :scope => [ :kind ]
-        }.merge(config)
+        }.merge!(config)
       end
 
       def compile
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 306d80b2df..837db05dcc 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -78,7 +78,7 @@ module ActiveSupport
     end
 
     def self.[](*args)
-      new.merge(Hash[*args])
+      new.merge!(Hash[*args])
     end
 
     alias_method :regular_writer, :[]= unless method_defined?(:regular_writer)