--- nmap/output.cc.orig	2007-12-15 09:54:07.000000000 -0800
+++ nmap/output.cc	2007-12-15 09:54:19.000000000 -0800
@@ -1904,7 +1904,7 @@
 
   /* Compares this record to another. First compare the directory names, then
      compare the file names. */
-  bool operator<(const struct data_file_record& other) {
+  bool operator<(const struct data_file_record& other) const {
     int cmp;
 
     cmp = dir.compare(other.dir);
