diff --git a/ChangeLog b/ChangeLog
index ebd9702222..8edf692b7d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Oct 10 18:42:23 2010  Akinori MUSHA  <knu@iDaemons.org>
+
+	* lib/set.rb (Set#replace): Apply a bit of optimization.
+
 Sun Oct 10 10:20:07 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in (RUBY_MINGW32): canonicalize as like mswin version.
diff --git a/lib/set.rb b/lib/set.rb
old mode 100644
new mode 100755
index 5e4e0878bd..5655c263ba
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -130,8 +130,8 @@ class Set
   # Replaces the contents of the set with the contents of the given
   # enumerable object and returns self.
   def replace(enum)
-    if enum.class == self.class
-      @hash.replace(enum.instance_eval { @hash })
+    if enum.instance_of?(self.class)
+      @hash.replace(enum.instance_variable_get(:@hash))
     else
       clear
       merge(enum)