diff --git a/lib/Support/raw_ostream.cpp b/lib/Support/raw_ostream.cpp
index 0fd0cdfa937..c2c55cff7ed 100644
--- a/lib/Support/raw_ostream.cpp
+++ b/lib/Support/raw_ostream.cpp
@@ -433,7 +433,7 @@ raw_ostream &raw_ostream::operator<<(const FormattedNumber &FN) {
     char *EndPtr = NumberBuffer+sizeof(NumberBuffer);
     char *CurPtr = EndPtr;
     bool Neg = (FN.DecValue < 0);
-    uint64_t N = Neg ? -FN.DecValue : FN.DecValue;
+    uint64_t N = Neg ? -static_cast<uint64_t>(FN.DecValue) : FN.DecValue;
     while (N) {
       *--CurPtr = '0' + char(N % 10);
       N /= 10;