diff --git a/js/src/jit/MIRGraph.h b/js/src/jit/MIRGraph.h
index 1eb44cb705e1..fe5cfe97e900 100644
--- a/js/src/jit/MIRGraph.h
+++ b/js/src/jit/MIRGraph.h
@@ -91,6 +91,9 @@ class MBasicBlock : public TempObject, public InlineListNode<MBasicBlock>
     // Mark this block (and only this block) as unreachable.
     void setUnreachable() {
         JS_ASSERT(!unreachable_);
+        setUnreachableUnchecked();
+    }
+    void setUnreachableUnchecked() {
         unreachable_ = true;
     }
     bool unreachable() const {
diff --git a/js/src/jit/RangeAnalysis.cpp b/js/src/jit/RangeAnalysis.cpp
index 59f202b24385..7fa995d492f4 100644
--- a/js/src/jit/RangeAnalysis.cpp
+++ b/js/src/jit/RangeAnalysis.cpp
@@ -1053,7 +1053,7 @@ MBeta::computeRange(TempAllocator &alloc)
     Range *range = Range::intersect(alloc, &opRange, comparison_, &emptyRange);
     if (emptyRange) {
         IonSpew(IonSpew_Range, "Marking block for inst %d unreachable", id());
-        block()->setUnreachable();
+        block()->setUnreachableUnchecked();
     } else {
         setRange(range);
     }