diff --git a/ChangeLog b/ChangeLog
index 43ddc4b033..b50c6225dd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jun 29 23:17:57 2011  WATANABE Hirofumi  <eban@ruby-lang.org>
+
+	* ext/openssl/ossl.h (OPENSSL_SYS_WIN32): support for mingw(msys).
+
 Wed Jun 29 23:09:14 2011  WATANABE Hirofumi  <eban@ruby-lang.org>
 
 	* ext/tk/extconf.rb (intptr_t, uintptr_t): support for the latest ActiveTcl with mingw.
diff --git a/ext/openssl/ossl.h b/ext/openssl/ossl.h
index d0edb7d5de..063ccef240 100644
--- a/ext/openssl/ossl.h
+++ b/ext/openssl/ossl.h
@@ -46,6 +46,7 @@ extern "C" {
 
 #if defined(_WIN32)
 #  define OSSL_NO_CONF_API 1
+#  define OPENSSL_SYS_WIN32 1
 #  ifdef USE_WINSOCK2
 #    include <winsock2.h>
 #  else