diff --git a/module/language/js-il/runtime.js b/module/language/js-il/runtime.js
index 49271bc9f..105247993 100644
--- a/module/language/js-il/runtime.js
+++ b/module/language/js-il/runtime.js
@@ -1162,6 +1162,9 @@ def_guile0("string-join", function (self, cont, strings) {
 
 // Fluids
 def_guile0("make-fluid", function (self, cont, val) {
+    if (val === undefined) {
+        val = scheme.FALSE;
+    }
     return cont(new scheme.Fluid(val));
 });