diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 70ed1c398ba..1019ad2594c 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -1319,8 +1319,14 @@ private:
   void moveEnteringDownFrom(SlotIndex OldIdx, IntRangePair& P) {
     LiveInterval* LI = P.first;
     LiveRange* LR = P.second;
+    // Extend the LiveRange if NewIdx is past the end.
     if (NewIdx > LR->end) {
-      moveKillFlags(LI->reg, LR->end, NewIdx);
+      // Move kill flags if OldIdx was not originally the end
+      // (otherwise LR->end points to an invalid slot).
+      if (LR->end.getRegSlot() != OldIdx.getRegSlot()) {
+        assert(LR->end > OldIdx && "LiveRange does not cover original slot");
+        moveKillFlags(LI->reg, LR->end, NewIdx);
+      }
       LR->end = NewIdx.getRegSlot();
     }
   }