diff --git a/js/src/jit-test/tests/ion/bug1128490.js b/js/src/jit-test/tests/ion/bug1128490.js
new file mode 100644
index 00000000000..09963b9b26e
--- /dev/null
+++ b/js/src/jit-test/tests/ion/bug1128490.js
@@ -0,0 +1,10 @@
+
+for (var i = 0; i < 1000; ++i) {
+    function isNotEmpty(obj) {
+        for (var i = 0 ; i < arguments.length; i++) {
+            minorgc();
+            var o = arguments[i];
+        }
+    };
+    isNotEmpty([1]);
+}
diff --git a/js/src/jit/BacktrackingAllocator.cpp b/js/src/jit/BacktrackingAllocator.cpp
index 36cafadf24e..f84336f7f1c 100644
--- a/js/src/jit/BacktrackingAllocator.cpp
+++ b/js/src/jit/BacktrackingAllocator.cpp
@@ -171,11 +171,16 @@ BacktrackingAllocator::canAddToGroup(VirtualRegisterGroup *group, BacktrackingVi
     return true;
 }
 
+static bool
+IsArgumentSlotDefinition(LDefinition *def)
+{
+    return def->policy() == LDefinition::FIXED && def->output()->isArgument();
+}
+
 static bool
 IsThisSlotDefinition(LDefinition *def)
 {
-    return def->policy() == LDefinition::FIXED &&
-           def->output()->isArgument() &&
+    return IsArgumentSlotDefinition(def) &&
            def->output()->toArgument()->index() < THIS_FRAME_ARGSLOT + sizeof(Value);
 }
 
@@ -199,6 +204,16 @@ BacktrackingAllocator::tryGroupRegisters(uint32_t vreg0, uint32_t vreg1)
             return true;
     }
 
+    // Registers which might spill to the frame's argument slots can only be
+    // grouped with other such registers if the frame might access those
+    // arguments through a lazy arguments object.
+    if ((IsArgumentSlotDefinition(reg0->def()) || IsArgumentSlotDefinition(reg1->def())) &&
+        graph.mir().entryBlock()->info().script()->argumentsAliasesFormals())
+    {
+        if (*reg0->def()->output() != *reg1->def()->output())
+            return true;
+    }
+
     VirtualRegisterGroup *group0 = reg0->group(), *group1 = reg1->group();
 
     if (!group0 && group1)
diff --git a/js/src/jit/JitFrames.cpp b/js/src/jit/JitFrames.cpp
index dd9fa059b48..43490b305d7 100644
--- a/js/src/jit/JitFrames.cpp
+++ b/js/src/jit/JitFrames.cpp
@@ -971,17 +971,21 @@ ReadAllocation(const JitFrameIterator &frame, const LAllocation *a)
 #endif
 
 static void
-MarkThisAndExtraActualArguments(JSTracer *trc, const JitFrameIterator &frame)
+MarkThisAndArguments(JSTracer *trc, const JitFrameIterator &frame)
 {
     // Mark |this| and any extra actual arguments for an Ion frame. Marking of
-    // formal arguments is taken care of by the frame's safepoint/snapshot.
+    // formal arguments is taken care of by the frame's safepoint/snapshot,
+    // except when the script's lazy arguments object aliases those formals,
+    // in which case we mark them as well.
 
     JitFrameLayout *layout = frame.jsFrame();
 
     size_t nargs = frame.numActualArgs();
     size_t nformals = 0;
-    if (CalleeTokenIsFunction(layout->calleeToken()))
-        nformals = CalleeTokenToFunction(layout->calleeToken())->nargs();
+    if (CalleeTokenIsFunction(layout->calleeToken())) {
+        JSFunction *fun = CalleeTokenToFunction(layout->calleeToken());
+        nformals = fun->nonLazyScript()->argumentsAliasesFormals() ? 0 : fun->nargs();
+    }
 
     Value *argv = layout->argv();
 
@@ -1023,7 +1027,7 @@ MarkIonJSFrame(JSTracer *trc, const JitFrameIterator &frame)
         ionScript = frame.ionScriptFromCalleeToken();
     }
 
-    MarkThisAndExtraActualArguments(trc, frame);
+    MarkThisAndArguments(trc, frame);
 
     const SafepointIndex *si = ionScript->getSafepointIndex(frame.returnAddressToFp());
 
@@ -1082,7 +1086,7 @@ MarkBailoutFrame(JSTracer *trc, const JitFrameIterator &frame)
 
     // We have to mark the list of actual arguments, as only formal arguments
     // are represented in the Snapshot.
-    MarkThisAndExtraActualArguments(trc, frame);
+    MarkThisAndArguments(trc, frame);
 
     // Under a bailout, do not have a Safepoint to only iterate over GC-things.
     // Thus we use a SnapshotIterator to trace all the locations which would be