# HG changeset patch
# Parent 56861f2edc5d3814d5341d49845eb98fc4669d45
diff --git a/js/src/jit/MCallOptimize.cpp b/js/src/jit/MCallOptimize.cpp
--- a/js/src/jit/MCallOptimize.cpp
+++ b/js/src/jit/MCallOptimize.cpp
@@ -1789,17 +1789,17 @@ IonBuilder::inlineUnsafeSetReservedSlot(
 
     callInfo.setImplicitlyUsedUnchecked();
 
     MStoreFixedSlot *store = MStoreFixedSlot::New(alloc(), callInfo.getArg(0), slot, callInfo.getArg(2));
     current->add(store);
     current->push(store);
 
     if (NeedsPostBarrier(info(), callInfo.getArg(2)))
-        current->add(MPostWriteBarrier::New(alloc(), callInfo.thisArg(), callInfo.getArg(2)));
+        current->add(MPostWriteBarrier::New(alloc(), callInfo.getArg(0), callInfo.getArg(2)));
 
     return InliningStatus_Inlined;
 }
 
 IonBuilder::InliningStatus
 IonBuilder::inlineUnsafeGetReservedSlot(CallInfo &callInfo)
 {
     if (callInfo.argc() != 2 || callInfo.constructing())