diff --git a/GL/glx/glxglcore.c b/GL/glx/glxglcore.c
index ecfa4d773..b50740c3c 100644
--- a/GL/glx/glxglcore.c
+++ b/GL/glx/glxglcore.c
@@ -258,12 +258,14 @@ __glXMesaScreenDestroy(__GLXscreen *screen)
     __GLXMESAscreen *mesaScreen = (__GLXMESAscreen *) screen;
     int i;
 
-    for (i = 0; i < mesaScreen->num_vis; i++) {
-	if (mesaScreen->xm_vis[i])
-	    XMesaDestroyVisual(mesaScreen->xm_vis[i]);
-    }
+    if (mesaScreen->xm_vis) {
+	for (i = 0; i < mesaScreen->num_vis; i++) {
+	    if (mesaScreen->xm_vis[i])
+		XMesaDestroyVisual(mesaScreen->xm_vis[i]);
+	}
 
-    xfree(mesaScreen->xm_vis);
+	xfree(mesaScreen->xm_vis);
+    }
 
     __glXScreenDestroy(screen);