diff --git a/ChangeLog b/ChangeLog
index 3e3451afe1..225cf65a31 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Tue Apr  3 09:56:20 2001  WATANABE Hirofumi  <eban@ruby-lang.org>
+
+	* ext/extmk.rb.in (create_makefile): create def file only if
+	  it does not yet exist.
+
+	* lib/mkmf.rb: ditto.
+
 Mon Apr  2 14:25:49 2001  Shugo Maeda <shugo@ruby-lang.org>
 
 	* lib/monitor.rb (wait): ensure reentrance.
diff --git a/ext/extmk.rb.in b/ext/extmk.rb.in
index a4d4c571b2..3b40772bf3 100644
--- a/ext/extmk.rb.in
+++ b/ext/extmk.rb.in
@@ -381,8 +381,10 @@ def create_makefile(target)
 
   defflag = ''
   if RUBY_PLATFORM =~ /cygwin|mingw/ and not $static
-    open(target + '.def', 'wb') do |f|
-      f.print "EXPORTS\n", "Init_", target, "\n"
+    if not File.exist? target + '.def'
+      open(target + '.def', 'wb') do |f|
+        f.print "EXPORTS\n", "Init_", target, "\n"
+      end
     end
     defflag = "--def=" + target + ".def"
   end
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 48c6a0f158..a9ce9b55bb 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -380,8 +380,10 @@ def create_makefile(target, srcdir = File.dirname($0))
 
   defflag = ''
   if RUBY_PLATFORM =~ /cygwin|mingw/
-    open(target + '.def', 'wb') do |f|
-      f.print "EXPORTS\n", "Init_", target, "\n"
+    if not File.exist? target + '.def'
+      open(target + '.def', 'wb') do |f|
+        f.print "EXPORTS\n", "Init_", target, "\n"
+      end
     end
     defflag = "--def=" + target + ".def"
   end