diff --git a/include/X11/Xlibint.h b/include/X11/Xlibint.h
index 603d05669..8596cb434 100644
--- a/include/X11/Xlibint.h	
+++ b/include/X11/Xlibint.h
@@ -389,23 +389,26 @@ struct _XLockPtrs {
 #define _XLockMutex_fn (*_XLockMutex_fn_p)
 #define _XUnlockMutex_fn (*_XUnlockMutex_fn_p)
 #define _Xglobal_lock (*_Xglobal_lock_p)
+#define X_LOCK_EXTERN __declspec(dllimport) extern
+#else
+#define X_LOCK_EXTERN extern
 #endif
 
 /* in XlibInt.c */
-extern void (*_XCreateMutex_fn)(
+X_LOCK_EXTERN void (*_XCreateMutex_fn)(
     LockInfoPtr /* lock */
 );
-extern void (*_XFreeMutex_fn)(
+X_LOCK_EXTERN void (*_XFreeMutex_fn)(
     LockInfoPtr /* lock */
 );
-extern void (*_XLockMutex_fn)(
+X_LOCK_EXTERN void (*_XLockMutex_fn)(
     LockInfoPtr	/* lock */
 #if defined(XTHREADS_WARN) || defined(XTHREADS_FILE_LINE)
     , char * /* file */
     , int /* line */
 #endif
 );
-extern void (*_XUnlockMutex_fn)(
+X_LOCK_EXTERN void (*_XUnlockMutex_fn)(
     LockInfoPtr	/* lock */
 #if defined(XTHREADS_WARN) || defined(XTHREADS_FILE_LINE)
     , char * /* file */
@@ -413,7 +416,7 @@ extern void (*_XUnlockMutex_fn)(
 #endif
 );
 
-extern LockInfoPtr _Xglobal_lock;
+X_LOCK_EXTERN LockInfoPtr _Xglobal_lock;
 
 #if defined(XTHREADS_WARN) || defined(XTHREADS_FILE_LINE)
 #define LockDisplay(d)	     if ((d)->lock_fns) (*(d)->lock_fns->lock_display)((d),__FILE__,__LINE__)