diff --git a/lib/CodeGen/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index ae14331d663..98fcc2e2529 100644
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/lib/CodeGen/PeepholeOptimizer.cpp
@@ -899,7 +899,11 @@ bool PeepholeOptimizer::optimizeCoalescableCopy(MachineInstr *MI) {
     if (!findNextSource(NewSrc, NewSubReg) || SrcReg == NewSrc)
       continue;
     // Rewrite source.
-    Changed |= CpyRewriter->RewriteCurrentSource(NewSrc, NewSubReg);
+    if (CpyRewriter->RewriteCurrentSource(NewSrc, NewSubReg)) {
+      // We may have extended the live-range of NewSrc, account for that.
+      MRI->clearKillFlags(NewSrc);
+      Changed = true;
+    }
   }
   // TODO: We could have a clean-up method to tidy the instruction.
   // E.g., v0 = INSERT_SUBREG v1, v1.sub0, sub0