Index: include/clang/Basic/SourceManager.h
===================================================================
--- include/clang/Basic/SourceManager.h	(revision 218299)
+++ include/clang/Basic/SourceManager.h	(working copy)
@@ -1677,7 +1677,7 @@
 public:
   explicit BeforeThanCompare(SourceManager &SM) : SM(SM) { }
 
-  bool operator()(SourceRange LHS, SourceRange RHS) {
+  bool operator()(SourceRange LHS, SourceRange RHS) const {
     return SM.isBeforeInTranslationUnit(LHS.getBegin(), RHS.getBegin());
   }
 };