diff --git a/engines/openbox/theme.c b/engines/openbox/theme.c
index 21042405..915ec9b9 100644
--- a/engines/openbox/theme.c
+++ b/engines/openbox/theme.c
@@ -164,7 +164,7 @@ gboolean read_mask(XrmDatabase db, char *rname, pixmap_mask **value)
         }
 
         if (ret) {
-            *value = pixmap_mask_new(w, h, b);
+            *value = pixmap_mask_new(w, h, (char*)b);
             XFree(b);
         }