diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp
index b8b7287..44a6d66 100644
--- a/lib/Basic/SourceManager.cpp
+++ b/lib/Basic/SourceManager.cpp
@@ -238,7 +238,7 @@
 /// for the position indicated.  This requires building and caching a table of
 /// line offsets for the MemoryBuffer, so this is not cheap: use only when
 /// about to emit a diagnostic.
-unsigned SourceManager::getLineNumber(SourceLocation Loc) {
+unsigned SourceManager::getLineNumber(SourceLocation Loc) const {
   unsigned FileID = Loc.getFileID();
   if (FileID == 0) return 0;