Index: cfe/trunk/lib/Driver/MSVCToolChain.cpp
===================================================================
--- cfe/trunk/lib/Driver/MSVCToolChain.cpp
+++ cfe/trunk/lib/Driver/MSVCToolChain.cpp
@@ -141,8 +141,8 @@
       nextKey++;
     size_t partialKeyLength = keyEnd - keyPath;
     char partialKey[256];
-    if (partialKeyLength > sizeof(partialKey))
-      partialKeyLength = sizeof(partialKey);
+    if (partialKeyLength >= sizeof(partialKey))
+      partialKeyLength = sizeof(partialKey) - 1;
     strncpy(partialKey, keyPath, partialKeyLength);
     partialKey[partialKeyLength] = '\0';
     HKEY hTopKey = NULL;