diff --git a/scheme/xlib/gcontext.scm b/scheme/xlib/gcontext.scm
index 4b3242d..e3c6051 100644
--- a/scheme/xlib/gcontext.scm
+++ b/scheme/xlib/gcontext.scm
@@ -276,7 +276,8 @@
 
 (define (make-gcontext-getter name)
   (lambda (gcontext)
-    (cdr (assq name (get-gcontext-values gcontext)))))
+    (let ((values (get-gcontext-values gcontext)))
+      (and values (cdr (assq name values))))))
 
 (define gcontext-function (make-gcontext-getter (gc-value function)))
 (define gcontext-plane-mask (make-gcontext-getter (gc-value plane-mask)))