Index: lib/Driver/ToolChains.cpp
===================================================================
--- lib/Driver/ToolChains.cpp
+++ lib/Driver/ToolChains.cpp
@@ -1230,7 +1230,9 @@
   GCCVersion GoodVersion = {VersionText.str(), -1, -1, -1, "", "", ""};
   if (First.first.getAsInteger(10, GoodVersion.Major) || GoodVersion.Major < 0)
     return BadVersion;
-  GoodVersion.MajorStr = First.first.str();
+  if (First.second.empty())
+    return GoodVersion;
+
   if (Second.first.getAsInteger(10, GoodVersion.Minor) || GoodVersion.Minor < 0)
     return BadVersion;
   GoodVersion.MinorStr = Second.first.str();
@@ -1238,6 +1240,7 @@
   // First look for a number prefix and parse that if present. Otherwise just
   // stash the entire patch string in the suffix, and leave the number
   // unspecified. This covers versions strings such as:
+  //   5        (handled above)
   //   4.4
   //   4.4.0
   //   4.4.x