diff -Naur bouml_4.3.4.orig/src/dialog/HelpDialog.cpp bouml_4.3.4/src/dialog/HelpDialog.cpp
--- bouml_4.3.4.orig/src/dialog/HelpDialog.cpp	2008-05-09 14:56:03.000000000 +0200
+++ bouml_4.3.4/src/dialog/HelpDialog.cpp	2008-05-25 17:48:32.000000000 +0200
@@ -132,7 +132,10 @@
   
   dirs[0] = ManualDir;
   DocDir = "";
-  
+
+  if (NavigatorPath.isEmpty())
+    NavigatorPath = "/usr/bin/xdg-open";
+
   for (index = (ManualDir.isEmpty()) ? 1 : 0;
        index != sizeof(dirs)/sizeof(*dirs);
        index += 1) {