diff --git a/lib/ostruct.rb b/lib/ostruct.rb
index 3c14454437..d3aea636a1 100644
--- a/lib/ostruct.rb
+++ b/lib/ostruct.rb
@@ -125,7 +125,7 @@ class OpenStruct
   #   data.each_pair.to_a  # => [[:country, "Australia"], [:population, 20000000]]
   #
   def each_pair
-    return to_enum __method__ unless block_given?
+    return to_enum(__method__) { @table.size } unless block_given?
     @table.each_pair{|p| yield p}
   end
 
diff --git a/test/ostruct/test_ostruct.rb b/test/ostruct/test_ostruct.rb
index 3c1d574e32..a28abe5211 100644
--- a/test/ostruct/test_ostruct.rb
+++ b/test/ostruct/test_ostruct.rb
@@ -113,6 +113,7 @@ class TC_OpenStruct < Test::Unit::TestCase
     os = OpenStruct.new(h)
     assert_equal '#<Enumerator: #<OpenStruct name="John Smith", age=70, pension=300>:each_pair>', os.each_pair.inspect
     assert_equal [[:name, "John Smith"], [:age, 70], [:pension, 300]], os.each_pair.to_a
+    assert_equal 3, os.each_pair.size
   end
 
   def test_eql_and_hash