diff --git a/graphics/grOGL1.c b/graphics/grOGL1.c
index 2ba1b1b0..ce3b4fac 100644
--- a/graphics/grOGL1.c
+++ b/graphics/grOGL1.c
@@ -1075,7 +1075,7 @@ GrOGLIconUpdate(w,text)
      XClassHint	class;
      char	*brack;
 
-     if (w->w_grdata == (ClientData)NULL) return;
+     if (w->w_grdata == PTR2CD(NULL)) return;
      class.res_name = "magic";
      class.res_class = "magic";
      XSetClassHint( grXdpy, wind, &class);
diff --git a/graphics/grOGL3.c b/graphics/grOGL3.c
index 28b28c77..8bcb2ee8 100644
--- a/graphics/grOGL3.c
+++ b/graphics/grOGL3.c
@@ -573,7 +573,7 @@ groglCreateBackingStore(MagWindow *w)
     if (w->w_client != DBWclientID) return;
 
     /* deferred */
-    if (w->w_grdata == (Window)NULL) return;
+    if (w->w_grdata == PTR2CD(NULL)) return;
 
     width = w->w_screenArea.r_xtop - w->w_screenArea.r_xbot;
     height = w->w_screenArea.r_ytop - w->w_screenArea.r_ybot;
diff --git a/graphics/grX11su1.c b/graphics/grX11su1.c
index 5c883489..0503387c 100644
--- a/graphics/grX11su1.c
+++ b/graphics/grX11su1.c
@@ -1442,7 +1442,7 @@ GrX11IconUpdate(w,text)
      XClassHint	class;
      char	*brack;
 
-     if (w->w_grdata == (ClientData)NULL) return;
+     if (w->w_grdata == PTR2CD(NULL)) return;
      class.res_name = "magic";
      class.res_class = "magic";
      XSetClassHint( grXdpy, wind, &class);
diff --git a/graphics/grX11su3.c b/graphics/grX11su3.c
index f46a2961..af24f390 100644
--- a/graphics/grX11su3.c
+++ b/graphics/grX11su3.c
@@ -393,7 +393,7 @@ grx11CreateBackingStore(MagWindow *w)
     if (w->w_client != DBWclientID) return;
 
     /* deferred */
-    if (w->w_grdata == (Window)NULL) return;
+    if (w->w_grdata == PTR2CD(NULL)) return;
 
     width = w->w_screenArea.r_xtop - w->w_screenArea.r_xbot;
     height = w->w_screenArea.r_ytop - w->w_screenArea.r_ybot;