diff --git a/ChangeLog b/ChangeLog
index ef74d8fe70..f5b32a3063 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun 17 07:46:50 2011  Eric Hodel  <drbrain@segment7.net>
+
+	* lib/benchmark.rb:  Document Benchmark::Tms#memberwise.  Patch by
+	  David Czarnecki.  [Ruby 1.9 - Bug #4873]
+
 Fri Jun 17 07:38:31 2011  Eric Hodel  <drbrain@segment7.net>
 
 	* lib/prettyprint.rb:  Improve documentation.  Patch by Ysiad
diff --git a/lib/benchmark.rb b/lib/benchmark.rb
index d2d2dcfaea..5ca9db1661 100644
--- a/lib/benchmark.rb
+++ b/lib/benchmark.rb
@@ -1,5 +1,4 @@
-=begin
-#
+#--
 # benchmark.rb - a performance benchmarking library
 #
 # $Id$
@@ -8,9 +7,8 @@
 #
 # Documentation by Gotoken (original RD), Lyle Johnson (RDoc conversion), and
 # Gavin Sinclair (editing).
+#++
 #
-=end
-
 # == Overview
 #
 # The Benchmark module provides methods for benchmarking Ruby code, giving
@@ -512,6 +510,15 @@ module Benchmark
     end
 
     protected
+    
+    #
+    # Returns a new Tms object obtained by memberwise operation +op+
+    # of the individual times for this Tms object with those of the other
+    # Tms object.
+    #
+    # +op+ can be a mathematical operation such as <tt>+</tt>, <tt>-</tt>,
+    # <tt>*</tt>, <tt>/</tt>
+    #
     def memberwise(op, x)
       case x
       when Benchmark::Tms