diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index cdaff2f..85fe474 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -947,13 +947,20 @@
 unsigned SourceManager::getColumnNumber(FileID FID, unsigned FilePos,
                                         bool *Invalid) const {
   bool MyInvalid = false;
-  const char *Buf = getBuffer(FID, &MyInvalid)->getBufferStart();
+  const llvm::MemoryBuffer *MemBuf = getBuffer(FID, &MyInvalid);
   if (Invalid)
     *Invalid = MyInvalid;
 
   if (MyInvalid)
     return 1;
 
+  const char *Buf = MemBuf->getBufferStart();
+  if (Buf + FilePos >= MemBuf->getBufferEnd()) {
+    if (Invalid)
+      *Invalid = MyInvalid;
+    return 1;
+  }
+
   unsigned LineStart = FilePos;
   while (LineStart && Buf[LineStart-1] != '\n' && Buf[LineStart-1] != '\r')
     --LineStart;