1 files changed, 2 insertions, 4 deletions
diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index 434a32b29b..e89b7e392e 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/activesupport/lib/active_support/core_ext/enumerable.rb
@@ -55,12 +55,10 @@ module Enumerable
   #  [].sum(Payment.new(0)) { |i| i.amount } # => Payment.new(0)
   #
   def sum(identity = 0, &block)
-    return identity unless size > 0
-
     if block_given?
-      map(&block).sum
+      map(&block).sum(identity)
     else
-      inject { |sum, element| sum + element }
+      inject { |sum, element| sum + element } || identity
     end
   end