diff --git a/Arrangement_2/examples/Arrangement_2/dual_lines.cpp b/Arrangement_2/examples/Arrangement_2/dual_lines.cpp
index 451164a409f..580b07a936d 100644
--- a/Arrangement_2/examples/Arrangement_2/dual_lines.cpp
+++ b/Arrangement_2/examples/Arrangement_2/dual_lines.cpp
@@ -18,7 +18,7 @@ int main (int argc, char **argv)
 {
   // Get the name of the input file from the command line, or use the default
   // points.dat file if no command-line parameters are given.
-  char * filename = (argc > 1) ? argv[1] : "points.dat";
+  const char * filename = (argc > 1) ? argv[1] : "points.dat";
 
   // Open the input file.
   std::ifstream     in_file (filename);