Index: sbbs.el
==================================================================
--- sbbs.el
+++ sbbs.el
@@ -72,11 +72,11 @@
   '((((background light)) :background "gray89" :extend t)
     (((background dark)) :background "gray11" :extend t))
   "Face for code blocks in threads.")
 
 (defface sbbs--variable-pitch
-  (if (x-list-fonts "Mona-")
+  (if (and (window-system) (x-list-fonts "Mona-"))
       '((nil :font "Mona"
              :inherit variable-pitch))
     '((nil :inherit variable-pitch)))
   "Face for code blocks in threads.")