diff --git a/js/src/mux.js b/js/src/mux.js
index 5058bf1..d9e5b6c 100644
--- a/js/src/mux.js
+++ b/js/src/mux.js
@@ -100,8 +100,8 @@ function computeAffectedPids(routingTable, delta) {
 }
 
 Mux.prototype.routeMessage = function (body) {
-  if (Trie.matchValue(this.routingTable, body) === null) {
-    return Trie.matchValue(this.routingTable, Patch.observe(body)) || Immutable.Set();
+  if (Trie.matchValue(this.routingTable, body, null) === null) {
+    return Trie.matchValue(this.routingTable, Patch.observe(body), null) || Immutable.Set();
   } else {
     // Some other stream has declared body
     return Immutable.Set();
diff --git a/js/src/trie.js b/js/src/trie.js
index 4bd8799..1cec10a 100644
--- a/js/src/trie.js
+++ b/js/src/trie.js
@@ -405,9 +405,7 @@ function subtract(o1, o2, subtractSuccessesOpt) {
 
 // Returns failureResult on failed match, otherwise the appropriate success
 // value contained in the trie r.
-function matchValue(r, v, failureResultOpt) {
-  var failureResult = failureResultOpt || null;
-
+function matchValue(r, v, failureResult) {
   var vs = Immutable.List.of(v);
 
   while (!is_emptyTrie(r)) {