diff --git a/lib/Lex/Preprocessor.cpp b/lib/Lex/Preprocessor.cpp
index eddff74..487b9d6 100644
--- a/lib/Lex/Preprocessor.cpp
+++ b/lib/Lex/Preprocessor.cpp
@@ -401,7 +401,7 @@
 /// LookUpIdentifierInfo - Given a tok::identifier token, look up the
 /// identifier information for the token and install it into the token.
 IdentifierInfo *Preprocessor::LookUpIdentifierInfo(Token &Identifier,
-                                                   const char *BufPtr) {
+                                                   const char *BufPtr) const {
   assert(Identifier.is(tok::identifier) && "Not an identifier!");
   assert(Identifier.getIdentifierInfo() == 0 && "Identinfo already exists!");