diff --git a/ChangeLog b/ChangeLog
index e01fdecb77..01ac47f68f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Aug  5 12:36:40 2005  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* lib/mkmf.rb (create_makefile): need to convert path separetor
+	  before invoking install command.
+
 Fri Aug  5 08:08:05 2005  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* eval.c (return_jump): fix "can't across thread" error message
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 157f20ce83..097be403e1 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1025,7 +1025,17 @@ static:		$(STATIC_LIB)#{$extout ? " install-rb" : ""}
     dest = "#{dir}/#{f}"
     mfile.print "install-so: #{dest}\n"
     unless $extout
-      mfile.print "#{dest}: #{f}\n\t$(INSTALL_PROG) #{f} #{dir}\n"
+      mfile.print "#{dest}: #{f}\n"
+      if (sep = config_string('BUILD_FILE_SEPARATOR'))
+        f.gsub!("/", sep)
+        dir.gsub!("/", sep)
+        sep = ":/="+sep
+        f.gsub!(/(\$\(\w+)(\))/) {$1+sep+$2}
+        f.gsub!(/(\$\{\w+)(\})/) {$1+sep+$2}
+        dir.gsub!(/(\$\(\w+)(\))/) {$1+sep+$2}
+        dir.gsub!(/(\$\{\w+)(\})/) {$1+sep+$2}
+      end
+      mfile.print "\t$(INSTALL_PROG) #{f} #{dir}\n"
     end
   end
   dirs << (dir = "$(RUBYLIBDIR)")