diff --git a/ChangeLog b/ChangeLog
index 20ac9549bc..23f22c59f8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Sep 14 04:07:09 2009  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
+
+	* lib/set.rb (==): Optimization; patch by Arthur Schreiber [ruby-core:17203]
+
 Mon Sep 14 03:30:23 2009  Alexander Zavorine  <alexandre.zavorine@nokia.com>
 
 	* symbian/pre-build: added rule to generate id.h for Symbian build.
diff --git a/lib/set.rb b/lib/set.rb
index 8f2bef91ba..f21ff14a70 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -327,13 +327,16 @@ class Set
 
   # Returns true if two sets are equal.  The equality of each couple
   # of elements is defined according to Object#eql?.
-  def ==(set)
-    equal?(set) and return true
-
-    set.is_a?(Set) && size == set.size or return false
-
-    hash = @hash.dup
-    set.all? { |o| hash.include?(o) }
+  def ==(other)
+    if self.equal?(other)
+      true
+    elsif other.instance_of?(self.class)
+      @hash == other.instance_variable_get(:@hash)
+    elsif other.is_a?(Set) && self.size == other.size
+      other.all? { |o| @hash.include?(o) }
+    else
+      false
+    end
   end
 
   def hash	# :nodoc: