diff --git a/owlps-udp-to-http/owlps-udp-to-http.c b/owlps-udp-to-http/owlps-udp-to-http.c
index 75befea..fcfce22 100644
--- a/owlps-udp-to-http/owlps-udp-to-http.c
+++ b/owlps-udp-to-http/owlps-udp-to-http.c
@@ -148,10 +148,10 @@ void parse_options(int argc, char **argv)
           print_usage() ;
           exit(0) ;
         case 'l' :
-          options.result_port = strtoul(optarg, NULL, 0) ;
+          options.result_port = strtoul(optarg, NULL, 10) ;
           break ;
         case 't' :
-          options.http_port = strtoul(optarg, NULL, 0) ;
+          options.http_port = strtoul(optarg, NULL, 10) ;
           break ;
         case 'q' :
           options.verbose = false ;