diff --git a/src/gui_w32.c b/src/gui_w32.c
index cc31c7c..ac0fb11 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -1772,7 +1772,7 @@
 # if !defined(_MSC_VER) || (_MSC_VER < 1400)
 /* Define HandleToLong for old MS and non-MS compilers if not defined. */
 #  ifndef HandleToLong
-#   define HandleToLong(h) ((long)(h))
+#   define HandleToLong(h) ((long)(intptr_t)(h))
 #  endif
 # endif
     /* set the v:windowid variable */