diff --git a/ChangeLog b/ChangeLog
index 908cd27a60..a0fba361d5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,8 +1,11 @@
-Sat Jun 26 11:05:39 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Sat Jun 26 11:07:20 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* configure.in (aix): -b must come at the start of the command line,
 	  and -e must not appear while testing libraries.  [ruby-talk:104501]
 
+	* lib/mkmf.rb (libpathflag, find_header, dir_config): quote directory
+	  names if necessary.  [ruby-talk:104505]
+
 Sat Jun 26 00:13:08 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (rb_fopen, rb_fdopen, rb_io_reopen): setvbuf() may return
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 0561c8bdb6..f132bf31b9 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -252,7 +252,7 @@ end
 def libpathflag(libpath=$LIBPATH)
   libpath.map{|x|
     (x == "$(topdir)" ? LIBPATHFLAG : LIBPATHFLAG+RPATHFLAG) % x
-  }.join
+  }.quote.join
 end
 
 def try_link0(src, opt="", &b)
@@ -541,10 +541,9 @@ def find_header(header, *paths)
     else
       found = false
       paths.each do |dir|
-        opt = "-I#{dir}"
+        opt = "-I#{dir}".quote
         if try_cpp(cpp_include(header), opt)
-          $INCFLAGS += " "
-          $INCFLAGS += opt
+          $INCFLAGS << " " << opt
           found = true
           break
         end
@@ -682,7 +681,7 @@ def dir_config(target, idefault=nil, ldefault=nil)
     idirs.collect! {|dir| "-I" + dir}
     idirs -= Shellwords.shellwords($CPPFLAGS)
     unless idirs.empty?
-      $CPPFLAGS = (idirs << $CPPFLAGS).join(" ")
+      $CPPFLAGS = (idirs.quote << $CPPFLAGS).join(" ")
     end
   end