diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
index 8aab4b2..f8e9208 100644
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -350,8 +350,8 @@
     unsigned long long PrevResult = Result;
     Result = Result*Radix+CharVal;
 
-    // Check for overflow.
-    if (Result < PrevResult)
+    // Check for overflow by shifting back and seeing if bits were lost.
+    if (Result/Radix < PrevResult)
       return true;
 
     Str = Str.substr(1);