diff --git a/js/src/frontend/Parser.cpp b/js/src/frontend/Parser.cpp
index 108fe4f6349a..1b2678954acc 100644
--- a/js/src/frontend/Parser.cpp
+++ b/js/src/frontend/Parser.cpp
@@ -471,6 +471,9 @@ FunctionBox::FunctionBox(ExclusiveContext *cx, ObjectBox* traceListHead, JSFunct
     usesApply(false),
     funCxFlags()
 {
+    // Functions created at parse time may be set singleton after parsing and
+    // baked into JIT code, so they must be allocated tenured. They are held by
+    // the JSScript so cannot be collected during a minor GC anyway.
     JS_ASSERT(fun->isTenured());
 
     if (!outerpc) {
diff --git a/js/src/ion/AsmJS.cpp b/js/src/ion/AsmJS.cpp
index 536218aa1ddc..e0b7bec06ec8 100644
--- a/js/src/ion/AsmJS.cpp
+++ b/js/src/ion/AsmJS.cpp
@@ -4664,9 +4664,10 @@ ParseFunction(ModuleCompiler &m, ParseNode **fnOut)
     if (!fn)
         return false;
 
+    // This flows into FunctionBox, so must be tenured.
     RootedFunction fun(m.cx(), NewFunction(m.cx(), NullPtr(), NULL, 0, JSFunction::INTERPRETED,
                                            m.cx()->global(), name, JSFunction::FinalizeKind,
-                                           GenericObject));
+                                           TenuredObject));
     if (!fun)
         return false;