diff --git a/mingw-w64-headers/include/ntddndis.h b/mingw-w64-headers/include/ntddndis.h
index 4469d9c..cbde001 100644
--- a/mingw-w64-headers/include/ntddndis.h
+++ b/mingw-w64-headers/include/ntddndis.h
@@ -820,7 +820,7 @@
   typedef struct _NDIS_802_11_TEST {
     ULONG Length;
     ULONG Type;
-    union {
+    __MINGW_EXTENSION union {
       NDIS_802_11_AUTHENTICATION_EVENT AuthenticationEvent;
       NDIS_802_11_RSSI RssiTrigger;
     };
@@ -1222,7 +1222,7 @@
 
   typedef struct _NDIS_GUID {
     GUID Guid;
-    union {
+    __MINGW_EXTENSION union {
       NDIS_OID Oid;
       NDIS_STATUS Status;
     };
diff --git a/mingw-w64-headers/include/olectl.h b/mingw-w64-headers/include/olectl.h
index 0ec5bde..6f9fed3 100644
--- a/mingw-w64-headers/include/olectl.h
+++ b/mingw-w64-headers/include/olectl.h
@@ -94,7 +94,7 @@
 typedef struct tagPICTDESC {
   UINT cbSizeofstruct;
   UINT picType;
-  union {
+  __MINGW_EXTENSION union {
     struct {
       HBITMAP hbitmap;
       HPALETTE hpal;
diff --git a/mingw-w64-headers/include/oledb.h b/mingw-w64-headers/include/oledb.h
index 92a5290..02c7f1b 100644
--- a/mingw-w64-headers/include/oledb.h
+++ b/mingw-w64-headers/include/oledb.h
@@ -531,16 +531,16 @@
 #ifndef DECIMAL_SETZERO
   typedef struct tagDEC {
     USHORT wReserved;
-    union {
-      struct {
+    __MINGW_EXTENSION union {
+      __MINGW_EXTENSION struct {
 	BYTE scale;
 	BYTE sign;
       };
       USHORT signscale;
     };
     ULONG Hi32;
-    union {
-      struct {
+    __MINGW_EXTENSION union {
+      __MINGW_EXTENSION struct {
 	ULONG Lo32;
 	ULONG Mid32;
       };
diff --git a/mingw-w64-headers/include/oledbguid.h b/mingw-w64-headers/include/oledbguid.h
index f60a31e..7c06362 100644
--- a/mingw-w64-headers/include/oledbguid.h
+++ b/mingw-w64-headers/include/oledbguid.h
@@ -17,8 +17,8 @@
 typedef unsigned long DBKIND;
 
 enum DBKINDENUM {
-  DBKIND_GUID_NAME = 0,DBKIND_GUID_PROPID = DBKIND_GUID_NAME + 1,DBKIND_NAME = DBKIND_GUID_PROPID + 1,DBKIND_PGUID_NAME = DBKIND_NAME + 1,
-  DBKIND_PGUID_PROPID = DBKIND_PGUID_NAME + 1,DBKIND_PROPID = DBKIND_PGUID_PROPID + 1,DBKIND_GUID = DBKIND_PROPID + 1
+  DBKIND_GUID_NAME = 0,DBKIND_GUID_PROPID,DBKIND_NAME,DBKIND_PGUID_NAME,
+  DBKIND_PGUID_PROPID,DBKIND_PROPID,DBKIND_GUID
 };
 
 typedef struct tagDBID {
diff --git a/mingw-w64-headers/include/patchapi.h b/mingw-w64-headers/include/patchapi.h
index c9f9692..fcfaec8 100644
--- a/mingw-w64-headers/include/patchapi.h
+++ b/mingw-w64-headers/include/patchapi.h
@@ -99,7 +99,7 @@
 
   typedef struct _PATCH_OLD_FILE_INFO {
     ULONG SizeOfThisStruct;
-    union {
+    __MINGW_EXTENSION union {
       LPCSTR OldFileNameA;
       LPCWSTR OldFileNameW;
       HANDLE OldFileHandle;
diff --git a/mingw-w64-headers/include/pdh.h b/mingw-w64-headers/include/pdh.h
index b5b4db7..019fb61 100644
--- a/mingw-w64-headers/include/pdh.h
+++ b/mingw-w64-headers/include/pdh.h
@@ -72,7 +72,7 @@
 
   typedef struct _PDH_FMT_COUNTERVALUE {
     DWORD CStatus;
-    union {
+    __MINGW_EXTENSION union {
       LONG longValue;
       double doubleValue;
       LONGLONG largeValue;
@@ -141,10 +141,10 @@
     DWORD_PTR dwUserData;
     DWORD_PTR dwQueryUserData;
     LPSTR szFullPath;
-    union {
+    __MINGW_EXTENSION union {
       PDH_DATA_ITEM_PATH_ELEMENTS_A DataItemPath;
       PDH_COUNTER_PATH_ELEMENTS_A CounterPath;
-      struct {
+      __MINGW_EXTENSION struct {
 	LPSTR szMachineName;
 	LPSTR szObjectName;
 	LPSTR szInstanceName;
@@ -167,10 +167,10 @@
     DWORD_PTR dwUserData;
     DWORD_PTR dwQueryUserData;
     LPWSTR szFullPath;
-    union {
+    __MINGW_EXTENSION union {
       PDH_DATA_ITEM_PATH_ELEMENTS_W DataItemPath;
       PDH_COUNTER_PATH_ELEMENTS_W CounterPath;
-      struct {
+      __MINGW_EXTENSION struct {
 	LPWSTR szMachineName;
 	LPWSTR szObjectName;
 	LPWSTR szInstanceName;
@@ -205,8 +205,8 @@
     LPSTR szBaseFileName;
     DWORD dwFileType;
     DWORD dwReserved;
-    union {
-      struct {
+    __MINGW_EXTENSION union {
+      __MINGW_EXTENSION struct {
 	DWORD PdlAutoNameInterval;
 	DWORD PdlAutoNameUnits;
 	LPSTR PdlCommandFilename;
@@ -216,7 +216,7 @@
 	FILETIME PdlLogStartTime;
 	FILETIME PdlLogEndTime;
       };
-      struct {
+      __MINGW_EXTENSION struct {
 	DWORD TlNumberOfBuffers;
 	DWORD TlMinimumBuffers;
 	DWORD TlMaximumBuffers;
@@ -240,8 +240,8 @@
     LPWSTR szBaseFileName;
     DWORD dwFileType;
     DWORD dwReserved;
-    union {
-      struct {
+    __MINGW_EXTENSION union {
+      __MINGW_EXTENSION struct {
 	DWORD PdlAutoNameInterval;
 	DWORD PdlAutoNameUnits;
 	LPWSTR PdlCommandFilename;
@@ -251,7 +251,7 @@
 	FILETIME PdlLogStartTime;
 	FILETIME PdlLogEndTime;
       };
-      struct {
+      __MINGW_EXTENSION struct {
 	DWORD TlNumberOfBuffers;
 	DWORD TlMinimumBuffers;
 	DWORD TlMaximumBuffers;
diff --git a/mingw-w64-headers/include/qossp.h b/mingw-w64-headers/include/qossp.h
index 9b37dea..be1a920 100644
--- a/mingw-w64-headers/include/qossp.h
+++ b/mingw-w64-headers/include/qossp.h
@@ -58,7 +58,7 @@
 
 typedef struct _RSVP_FILTERSPEC {
   FilterType Type;
-  union {
+  __MINGW_EXTENSION union {
     RSVP_FILTERSPEC_V4 FilterSpecV4;
     RSVP_FILTERSPEC_V6 FilterSpecV6;
     RSVP_FILTERSPEC_V6_FLOW FilterSpecV6Flow;
@@ -151,7 +151,7 @@
   ULONG Length;
   SERVICETYPE Service;
   AD_GENERAL_PARAMS Overrides;
-  union {
+  __MINGW_EXTENSION union {
     AD_GUARANTEED Guaranteed;
     PARAM_BUFFER ParamBuffer[1];
   };
diff --git a/mingw-w64-headers/include/resapi.h b/mingw-w64-headers/include/resapi.h
index ac176d8..5351e12 100644
--- a/mingw-w64-headers/include/resapi.h
+++ b/mingw-w64-headers/include/resapi.h
@@ -82,7 +82,7 @@
   typedef struct CLRES_FUNCTION_TABLE {
     DWORD TableSize;
     DWORD Version;
-    union {
+    __MINGW_EXTENSION union {
       CLRES_V1_FUNCTIONS V1Functions;
     };
   } CLRES_FUNCTION_TABLE,*PCLRES_FUNCTION_TABLE;
@@ -111,7 +111,7 @@
     LPWSTR Name;
     LPWSTR KeyName;
     DWORD Format;
-    union {
+    __MINGW_EXTENSION union {
       DWORD_PTR DefaultPtr;
       DWORD Default;
       LPVOID lpDefault;
diff --git a/mingw-w64-headers/include/rtmv2.h b/mingw-w64-headers/include/rtmv2.h
index 54acd29..a03f44c 100644
--- a/mingw-w64-headers/include/rtmv2.h
+++ b/mingw-w64-headers/include/rtmv2.h
@@ -152,8 +152,8 @@
 #define RTM_NEXTHOP_FLAGS_DOWN 0x0002
 
   typedef struct _RTM_ENTITY_ID {
-    union {
-      struct {
+    __MINGW_EXTENSION union {
+      __MINGW_EXTENSION struct {
 	ULONG EntityProtocolId;
 	ULONG EntityInstanceId;
       };