diff --git a/ChangeLog b/ChangeLog
index 906ca106e0..2114d625f2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Feb 21 21:20:17 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (create_makefile, install_files): honor srcprefix
+	  argument if given.  [ruby-dev:40449]
+
 Sun Feb 21 13:29:57 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/rubygems/rubygems_version.rb: outdated.  [ruby-core:28275]
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index fc9353e5cd..3b667a68bf 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -624,7 +624,7 @@ end
 def install_files(mfile, ifiles, map = nil, srcprefix = nil)
   ifiles or return
   ifiles.empty? and return
-  srcprefix ||= '$(srcdir)'
+  srcprefix ||= "$(srcdir)/#{srcprefix}".chomp('/')
   RbConfig::expand(srcdir = srcprefix.dup)
   dirs = []
   path = Hash.new {|h, i| h[i] = dirs.push([i])[-1]}
@@ -1684,7 +1684,7 @@ def create_makefile(target, srcprefix = nil)
     target_prefix = ""
   end
 
-  srcprefix = "$(srcdir)/#{srcprefix}".chomp('/')
+  srcprefix ||= "$(srcdir)/#{srcprefix}".chomp('/')
   RbConfig.expand(srcdir = srcprefix.dup)
 
   ext = ".#{$OBJEXT}"