diff --git a/c/xlib/gcontext.c b/c/xlib/gcontext.c
index 6558601..48d5c2d 100644
--- a/c/xlib/gcontext.c
+++ b/c/xlib/gcontext.c
@@ -2,7 +2,7 @@
 #include "scheme48.h"
 
 unsigned long AList_To_GCValues(s48_value alist, XGCValues* GCV) {
-  unsigned long mask;
+  unsigned long mask = 0;
   s48_value l;
   char* cname;
   s48_value name, value;