diff --git a/langkit/langkit_lexer.cpp b/langkit/langkit_lexer.cpp
index c0394eb3..0550f88e 100644
--- a/langkit/langkit_lexer.cpp
+++ b/langkit/langkit_lexer.cpp
@@ -9,7 +9,7 @@ Lexer Lexer::operator<<(const Pattern &p) {
     return *this;
 }
 
-std::vector<Token> Lexer::lex(const std::string &input) {
+std::vector<Token> Lexer::lex(const std::string &input, const char *filename) {
     std::vector<Pattern>::iterator iter, end;
     std::vector<Token> retval;
     bool found;
@@ -23,7 +23,7 @@ std::vector<Token> Lexer::lex(const std::string &input) {
         for (iter = lex_patterns.begin(), end = lex_patterns.end(); iter != end; ++iter) {
             boost::match_results<std::string::const_iterator> what;
             if (regex_search(input_iter, input.end(), what, iter->regex, boost::match_continuous)) {
-                Token t(what[0], iter->identifier);
+                Token t(what[0], iter->identifier, filename);
                 t.start.column = current_col;
                 t.start.line = current_line;
                 current_col += t.text.size();
diff --git a/langkit/langkit_lexer.hpp b/langkit/langkit_lexer.hpp
index 4c8a959e..72c5251b 100644
--- a/langkit/langkit_lexer.hpp
+++ b/langkit/langkit_lexer.hpp
@@ -10,12 +10,11 @@
 struct File_Position {
     int line;
     int column;
-    char *filename;
 
-    File_Position(int file_line, int file_column, char *fname)
-        : line(file_line), column(file_column), filename(fname) { }
+    File_Position(int file_line, int file_column)
+        : line(file_line), column(file_column) { }
 
-    File_Position() : line(0), column(0), filename(NULL) { }
+    File_Position() : line(0), column(0) { }
 };
 
 struct Pattern {
@@ -28,11 +27,12 @@ struct Pattern {
 struct Token {
     std::string text;
     int identifier;
+    const char *filename;
     File_Position start, end;
 
     std::vector<Token> children;
 
-    Token(const std::string &token_text, int id) : text(token_text), identifier(id) { }
+    Token(const std::string &token_text, int id, const char *fname) : text(token_text), identifier(id), filename(fname) { }
 };
 
 struct Lexer {
@@ -42,7 +42,7 @@ struct Lexer {
     std::vector<Pattern> line_sep_patterns;
 
     Lexer operator<<(const Pattern &p);
-    std::vector<Token> lex(const std::string &input);
+    std::vector<Token> lex(const std::string &input, const char *fname);
 
     void set_skip(const Pattern &p);
     void set_line_sep(const Pattern &p);
diff --git a/langkit/main.cpp b/langkit/main.cpp
index 0ac5ff0b..67d9be16 100644
--- a/langkit/main.cpp
+++ b/langkit/main.cpp
@@ -14,7 +14,7 @@ class TokenType { public: enum Type { Whitespace, Identifier, Number, Operator,
     Square_Open, Square_Close, Curly_Open, Curly_Close, Comma, Quoted_String, Single_Quoted_String, Carriage_Return, Semicolon }; };
 
 void debug_print(Token &token) {
-    std::cout << "Token: " << token.text << "(" << token.identifier << ") @ (" << token.start.column
+    std::cout << "Token: " << token.text << "(" << token.identifier << ") @ " << token.filename << ": ("  << token.start.column
         << ", " << token.start.line << ") to (" << token.end.column << ", " << token.end.line << ") " << std::endl;
 }
 void debug_print(std::vector<Token> &tokens) {
@@ -84,7 +84,7 @@ int main(int argc, char *argv[]) {
         std::cout << "Expression> ";
         std::getline(std::cin, input);
         while (input != "quit") {
-            std::vector<Token> tokens = lexer.lex(input);
+            std::vector<Token> tokens = lexer.lex(input, "INPUT");
             debug_print(tokens);
             parse(tokens);
 
@@ -93,7 +93,7 @@ int main(int argc, char *argv[]) {
         }
     }
     else {
-        std::vector<Token> tokens = lexer.lex(load_file(argv[1]));
+        std::vector<Token> tokens = lexer.lex(load_file(argv[1]), argv[1]);
         debug_print(tokens);
     }
 }