1 files changed, 2 insertions, 2 deletions
diff --git a/lib/js/urweb.js b/lib/js/urweb.js
index d0322bff..39701b4d 100644
--- a/lib/js/urweb.js
+++ b/lib/js/urweb.js
@@ -30,8 +30,8 @@ function whine(msg) {
   throw msg;
 }
 
-function pf() {
-  whine("Pattern match failure");
+function pf(loc) {
+  whine("Pattern match failure (" + loc + ")");
 }
 
 function runHandlers(kind, ls, arg) {