diff --git a/ChangeLog b/ChangeLog
index 08309a8acf..22e5f9f758 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Jun 19 14:46:18 2002  WATANABE Hirofumi  <eban@ruby-lang.org>
+
+	* ext/extmk.rb, lib/mkmf.rb (xsystem): open the log file if xsystem
+	  is called.
+
 Mon Jun 17 10:51:37 2002  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
 
 	* dln.c (dln_load): need to preserve dln_strerror() result,
diff --git a/ext/extmk.rb.in b/ext/extmk.rb.in
index 4dc2339acb..244b3bc13f 100644
--- a/ext/extmk.rb.in
+++ b/ext/extmk.rb.in
@@ -78,18 +78,21 @@ end
 LINK = "@CC@ #{OUTFLAG}conftest -I#$topdir -I#$top_srcdir #{CFLAGS} @LDFLAGS@ %s %s %s conftest.c %s %s @LIBS@"
 CPP = "@CPP@ @CPPFLAGS@ -I#$topdir -I#$top_srcdir #{CFLAGS} %s %s %s conftest.c"
 
-$log = open('extmk.log', 'w')
-
+$log = nil
 $orgerr = $stderr.dup
 $orgout = $stdout.dup
+
 def xsystem command
   if $DEBUG
     puts command
+    $stdout.flush
     return system(command)
   end
+  $log ||= open(File.join($topdir, 'ext', 'extmk.log'), 'w')
   $stderr.reopen($log) 
   $stdout.reopen($log) 
   puts command
+  $stdout.flush
   r = system(command)
   $stderr.reopen($orgerr)
   $stdout.reopen($orgout)
@@ -712,6 +715,7 @@ for d in Dir["#{ext_prefix}/**/*"]
       load "#{$top_srcdir}/ext/aix_mksym.rb"
     end
   end
+  $stdout.flush
   extmake(d)
 end
 
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 5a540187dc..89a88cddb4 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -57,8 +57,6 @@ elsif RUBY_PLATFORM =~ /-nextstep|-rhapsody|-darwin/
   CFLAGS.gsub!( /-arch\s\w*/, '' )
 end
 
-$log = open('mkmf.log', 'w')
-
 if /mswin32/ =~ RUBY_PLATFORM
   OUTFLAG = '-Fe'
 else
@@ -78,17 +76,22 @@ def rm_f(*files)
   end
 end
 
+$log = nil
+
 $orgerr = $stderr.dup
 $orgout = $stdout.dup
 def xsystem command
   Config.expand(command)
   if $DEBUG
     puts command
+    $stdout.flush
     return system(command)
   end
+  $log ||= open('mkmf.log', 'w')
   $stderr.reopen($log) 
   $stdout.reopen($log) 
   puts command
+  $stdout.flush
   r = system(command)
   $stderr.reopen($orgerr)
   $stdout.reopen($orgout)