diff --git a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_image.cxx b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_image.cxx
index 9a2180910..868d81ec8 100644
--- a/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_image.cxx
+++ b/src/drivers/Quartz/Fl_Quartz_Graphics_Driver_image.cxx
@@ -302,7 +302,7 @@ void Fl_Quartz_Graphics_Driver::uncache(Fl_RGB_Image*, fl_uintptr_t &id_, fl_uin
     if (mask_) *(bool*)mask_ = false;
     CGImageRelease((CGImageRef)id_);
     id_ = 0;
-    mask_ = NULL;
+    mask_ = 0;
   }
 }