1 files changed, 9 insertions, 0 deletions
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 4c1a0bb2d5fb..bc6c3287c79d 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -27,6 +27,15 @@ struct Pos
     Pos() : line(0), column(0) { };
     Pos(const string & file, unsigned int line, unsigned int column)
         : file(file), line(line), column(column) { };
+    bool operator < (const Pos & p2) const
+    {
+        int d = file.compare(p2.file);
+        if (d < 0) return true;
+        if (d > 0) return false;
+        if (line < p2.line) return true;
+        if (line > p2.line) return false;
+        return column < p2.column;
+    }
 };
 
 extern Pos noPos;