diff --git a/lib/Transforms/Scalar/ScalarReplAggregates.cpp b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
index d36a18f21c6..4e348687777 100644
--- a/lib/Transforms/Scalar/ScalarReplAggregates.cpp
+++ b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -574,8 +574,8 @@ void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI,
     // transform it into a store of the expanded constant value.
     if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
       assert(MSI->getRawDest() == Ptr && "Consistency error!");
-      signed SNumBytes = cast<ConstantInt>(MSI->getLength())->getSExtValue();
-      if (SNumBytes > 0) {
+     int64_t SNumBytes = cast<ConstantInt>(MSI->getLength())->getSExtValue();
+      if (SNumBytes > 0 && (SNumBytes >> 32) == 0) {
         unsigned NumBytes = static_cast<unsigned>(SNumBytes);
         unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();