diff --git a/js/src/jit-test/tests/ion/bug921035.js b/js/src/jit-test/tests/ion/bug921035.js
new file mode 100644
index 00000000000..33b8c5c5a87
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug921035.js
@@ -0,0 +1,14 @@
+// |jit-test| error: TypeError
+
+function $ERROR() {}
+function testMultipleArgumentsObjects() {
+    var testargs = arguments;
+    var f = function (which) {
+        var args = [ testargs ];
+        return args[which][0];
+    };
+    var arr = [0, 0, 0, 0, 1];
+    for (var i = 0; i < arr.length; i++)
+        $ERROR[i] = f(arr[i]);
+}
+testMultipleArgumentsObjects()
diff --git a/js/src/jit/IonAnalysis.cpp b/js/src/jit/IonAnalysis.cpp
index a2c9f4a38f0..c21bc213c77 100644
--- a/js/src/jit/IonAnalysis.cpp
+++ b/js/src/jit/IonAnalysis.cpp
@@ -211,16 +211,25 @@ IsPhiObservable(MPhi *phi, Observability observe)
         break;
     }
 
-    // If the Phi is of the |this| value, it must always be observable.
     uint32_t slot = phi->slot();
     CompileInfo &info = phi->block()->info();
-    if (info.fun() && slot == info.thisSlot())
+    JSFunction *fun = info.fun();
+
+    // If the Phi is of the |this| value, it must always be observable.
+    if (fun && slot == info.thisSlot())
+        return true;
+
+    // If the function is heavyweight, and the Phi is of the |scopeChain|
+    // value, and the function may need an arguments object, then make sure
+    // to preserve the scope chain, because it may be needed to construct the
+    // arguments object during bailout.
+    if (fun && fun->isHeavyweight() && info.hasArguments() && slot == info.scopeChainSlot())
         return true;
 
     // If the Phi is one of the formal argument, and we are using an argument
     // object in the function. The phi might be observable after a bailout.
     // For inlined frames this is not needed, as they are captured in the inlineResumePoint.
-    if (info.fun() && info.hasArguments()) {
+    if (fun && info.hasArguments()) {
         uint32_t first = info.firstArgSlot();
         if (first <= slot && slot - first < info.nargs()) {
             // If arguments obj aliases formals, then the arg slots will never be used.