diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index eae964bc2e64a61f6d618aac3a64874d45f8d9a8..9a893157ea36d20fe207c6a654f4995e2a4ab308 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -114,11 +114,15 @@ def sum(identity = nil)
 # just calling the compat method in the first place.
 if Array.instance_methods(false).include?(:sum) && !(%w[a].sum rescue false)
   class Array
-    remove_method :sum
+    alias :orig_sum :sum
 
-    def sum(*args) #:nodoc:
-      # Use Enumerable#sum instead.
-      super
+    def sum(init = nil, &block) #:nodoc:
+      if init.is_a?(Numeric) || first.is_a?(Numeric)
+        init ||= 0
+        orig_sum(init, &block)
+      else
+        super
+      end
     end
   end
 end