diff --git a/src/w32fns.c b/src/w32fns.c
index 7d288ce7bd5..ace8d1016a5 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -305,10 +305,12 @@ static unsigned int sound_type = 0xFFFFFFFF;
 /* Special virtual key code for indicating "any" key.  */
 #define VK_ANY 0xFF
 
-#ifndef WM_WTSSESSION_CHANGE
+#ifdef WINDOWSNT
+# ifndef WM_WTSSESSION_CHANGE
 /* 32-bit MinGW does not define these constants.  */
-# define WM_WTSSESSION_CHANGE  0x02B1
-# define WTS_SESSION_LOCK      0x7
+#  define WM_WTSSESSION_CHANGE  0x02B1
+#  define WTS_SESSION_LOCK      0x7
+# endif
 #endif
 
 #ifndef WS_EX_NOACTIVATE
diff --git a/src/w32xfns.c b/src/w32xfns.c
index 853c8368118..b248697e658 100644
--- a/src/w32xfns.c
+++ b/src/w32xfns.c
@@ -22,9 +22,11 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <stdio.h>
 #include <windows.h>
 #include <windowsx.h>
+
+#ifdef WINDOWSNT
 /* Override API version to get the required functionality.  */
-#undef _WIN32_WINNT
-#define _WIN32_WINNT 0x0501
+# undef _WIN32_WINNT
+# define _WIN32_WINNT 0x0501
 /* mingw.org's MinGW headers mistakenly omit this enumeration: */
 # ifndef MINGW_W64
 typedef enum _WTS_VIRTUAL_CLASS {
@@ -33,6 +35,7 @@ typedef enum _WTS_VIRTUAL_CLASS {
 } WTS_VIRTUAL_CLASS;
 # endif
 #include <wtsapi32.h>	/* for WM_WTSSESSION_CHANGE, WTS_SESSION_LOCK */
+#endif	/* WINDOWSNT */
 
 #include "lisp.h"
 #include "frame.h"
@@ -426,10 +429,12 @@ drain_message_queue (void)
     {
       switch (msg.message)
 	{
+#ifdef WINDOWSNT
 	case WM_WTSSESSION_CHANGE:
 	  if (msg.wParam == WTS_SESSION_LOCK)
 	    reset_w32_kbdhook_state ();
 	  break;
+#endif
 	case WM_EMACS_FILENOTIFY:
 	  retval = 1;
 	  break;