diff --git a/MagickCore/cache-private.h b/MagickCore/cache-private.h
index 51afa32..b106cc6 100644
--- a/MagickCore/cache-private.h
+++ b/MagickCore/cache-private.h
@@ -116,7 +116,8 @@
     alpha_trait;
 
   MagickBooleanType
-    mask;
+    read_mask,
+    write_mask;
 
   size_t
     columns,