diff --git a/ChangeLog b/ChangeLog
index de5419aedb..52fd761eab 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Sep 23 12:11:26 2013  Masaki Matsushita  <glass.saga@gmail.com>
+
+	* hash.c (env_each_pair): do not call rb_assoc_new() if
+	  it isn't needed.
+
 Mon Sep 23 10:42:30 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* test/ruby/test_module.rb (TestModule#test_include_toplevel): test
diff --git a/hash.c b/hash.c
index 1098118737..8c72da2c05 100644
--- a/hash.c
+++ b/hash.c
@@ -2901,8 +2901,15 @@ env_each_pair(VALUE ehash)
     }
     FREE_ENVIRON(environ);
 
-    for (i=0; i<RARRAY_LEN(ary); i+=2) {
-	rb_yield(rb_assoc_new(RARRAY_AREF(ary, i), RARRAY_AREF(ary, i+1)));
+    if (rb_block_arity() > 1) {
+	for (i=0; i<RARRAY_LEN(ary); i+=2) {
+	    rb_yield_values(2, RARRAY_AREF(ary, i), RARRAY_AREF(ary, i+1));
+	}
+    }
+    else {
+	for (i=0; i<RARRAY_LEN(ary); i+=2) {
+	    rb_yield(rb_assoc_new(RARRAY_AREF(ary, i), RARRAY_AREF(ary, i+1)));
+	}
     }
     return ehash;
 }