diff --git a/winsup/w32api/ChangeLog b/winsup/w32api/ChangeLog
index f21aa6c32..c5f301cd8 100644
--- a/winsup/w32api/ChangeLog
+++ b/winsup/w32api/ChangeLog
@@ -1,3 +1,9 @@
+2011-03-04  Chris Sutcliffe  <ir0nh34d@users.sourceforge.net>
+
+	* include/winbase.h (__MINGW_EXTENSION): Define.
+	(OVERLAPPED): Add __MINGW_EXTENSION around nameless union /
+	struct to correct issue with -std=c99.
+
 2011-03-02  Corinna Vinschen  <corinna@vinschen.de>
 
 	* include/ddk/winddk.h (TIMER_INFORMATION_CLASS): Define.
diff --git a/winsup/w32api/include/winbase.h b/winsup/w32api/include/winbase.h
index a3ce7784e..18f1b7e56 100644
--- a/winsup/w32api/include/winbase.h
+++ b/winsup/w32api/include/winbase.h
@@ -4,6 +4,12 @@
 #pragma GCC system_header
 #endif
 
+#ifdef __GNUC__
+#define __MINGW_EXTENSION __extension__
+#else
+#define __MINGW_EXTENSION
+#endif
+
 #ifndef WINBASEAPI
 #ifdef __W32API_USE_DLLIMPORT__
 #define WINBASEAPI DECLSPEC_IMPORT
@@ -833,8 +839,8 @@ typedef struct _DEBUG_EVENT {
 typedef struct _OVERLAPPED {
 	ULONG_PTR Internal;
 	ULONG_PTR InternalHigh;
-	union {
-		struct {
+	__MINGW_EXTENSION union {
+		__MINGW_EXTENSION struct {
 	DWORD Offset;
 	DWORD OffsetHigh;
 	};