diff --git a/owlps-listener/owlps-listenerd.c b/owlps-listener/owlps-listenerd.c
index 80c0953..d91bfaa 100644
--- a/owlps-listener/owlps-listenerd.c
+++ b/owlps-listener/owlps-listenerd.c
@@ -529,6 +529,8 @@ int parse_command_line(int argc, char **argv)
 int parse_main_options(int argc, char **argv)
 {
   int opt ;
+  long arg_long ; // Integer value of optarg
+  char *endptr ; // Return value of strtol()
 
   optind = 1 ; // Rewind argument parsing
 
@@ -559,7 +561,7 @@ int parse_main_options(int argc, char **argv)
           break ;
         case 'H' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_HELLO_PORT(strtol(optarg, NULL, 0)) ;
+          SET_AUTOCALIBRATION_HELLO_PORT(strtol(optarg, NULL, 10)) ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'i' :
@@ -580,27 +582,27 @@ int parse_main_options(int argc, char **argv)
 #endif // OWLPS_LISTENER_KEEPS_MONITOR
           break ;
         case 'l' :
-          SET_LISTENING_PORT(strtol(optarg, NULL, 0)) ;
+          SET_LISTENING_PORT(strtol(optarg, NULL, 10)) ;
           break ;
         case 'm' :
           SET_MODE(optarg[0]) ;
           break ;
         case 'n' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_NBPKT(strtol(optarg, NULL, 0)) ;
+          SET_AUTOCALIBRATION_NBPKT(strtol(optarg, NULL, 10)) ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'O' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_ORDER_PORT(strtol(optarg, NULL, 0)) ;
+          SET_AUTOCALIBRATION_ORDER_PORT(strtol(optarg, NULL, 10)) ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'p' :
-          SET_AGGREGATION_PORT(strtol(optarg, NULL, 0)) ;
+          SET_AGGREGATION_PORT(strtol(optarg, NULL, 10)) ;
           break ;
         case 'P' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_REQUEST_PORT(strtol(optarg, NULL, 0)) ;
+          SET_AUTOCALIBRATION_REQUEST_PORT(strtol(optarg, NULL, 10)) ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'q' :
@@ -614,12 +616,22 @@ int parse_main_options(int argc, char **argv)
           break ;
         case 't' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_DELAY(strtol(optarg, NULL, 0)) ;
+          arg_long = strtol(optarg, &endptr, 10) ;
+          if (endptr != optarg)
+            SET_AUTOCALIBRATION_DELAY(arg_long) ;
+          else
+            fprintf(stderr, "Warning! Bad autocalibration_delay:"
+                    " failing back to the default value.\n") ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'T' :
 #ifdef OWLPS_LISTENER_USES_PTHREAD
-          SET_AUTOCALIBRATION_HELLO_DELAY(strtol(optarg, NULL, 0)) ;
+          arg_long = strtol(optarg, &endptr, 10) ;
+          if (endptr != optarg)
+            SET_AUTOCALIBRATION_HELLO_DELAY(arg_long) ;
+          else
+            fprintf(stderr, "Warning! Bad autocalibration_hello_delay:"
+                    " failing back to the default value.\n") ;
 #endif // OWLPS_LISTENER_USES_PTHREAD
           break ;
         case 'v' :
@@ -641,28 +653,69 @@ int parse_main_options(int argc, char **argv)
 
 
 #ifdef OWLPS_LISTENER_USES_PTHREAD
+/* Parses remaining arguments (possible calibration data) */
 int parse_calibration_data(int argc, char **argv)
 {
-  /* Parse remaining arguments (possible calibration data) */
-  if (argc - optind != 0)
+  /* No more arguments to parse */
+  if (argc - optind == 0)
+    return 0 ;
+
+  /* Exactly 4 more arguments */
+  if (argc - optind == 4)
     {
-      if (argc - optind == 4)
+      char *endptr ;
+      unsigned long arg_ulong ;
+      double arg_double ;
+
+      coordinates_provided = true ;
+
+      arg_ulong = strtoul(argv[optind], &endptr, 10) ;
+      if (endptr == argv[optind])
         {
-          coordinates_provided = true ;
-          SET_MY_DIRECTION(strtoul(argv[optind++], NULL, 0)) ;
-          SET_MY_POSITION_X(strtod(argv[optind++], NULL)) ;
-          SET_MY_POSITION_Y(strtod(argv[optind++], NULL)) ;
-          SET_MY_POSITION_Z(strtod(argv[optind], NULL)) ;
+          fprintf(stderr,
+                  "Error in calibration data: wrong direction!\n") ;
+          goto error ;
         }
-      else // Bad number of arguments
+      SET_MY_DIRECTION(arg_ulong) ;
+      optind++ ;
+
+      arg_double = strtod(argv[optind], &endptr) ;
+      if (endptr == argv[optind])
         {
-          print_usage() ;
-          owl_run = false ;
-          return OWL_ERR_BAD_USAGE ;
+          fprintf(stderr,
+                  "Error in calibration data: wrong X coordinate!\n") ;
+          goto error ;
         }
+      SET_MY_POSITION_X(arg_double) ;
+      optind++ ;
+
+      arg_double = strtod(argv[optind], &endptr) ;
+      if (endptr == argv[optind])
+        {
+          fprintf(stderr,
+                  "Error in calibration data: wrong Y coordinate!\n") ;
+          goto error ;
+        }
+      SET_MY_POSITION_Y(arg_double) ;
+      optind++ ;
+
+      arg_double = strtod(argv[optind], &endptr) ;
+      if (endptr == argv[optind])
+        {
+          fprintf(stderr,
+                  "Error in calibration data: wrong Z coordinate!\n") ;
+          goto error ;
+        }
+      SET_MY_POSITION_Z(arg_double) ;
+
+      return 0 ; // No error occurred
     }
 
-  return 0 ;
+  /* Bad number of arguments or parse error */
+ error:
+  print_usage() ;
+  owl_run = false ;
+  return OWL_ERR_BAD_USAGE ;
 }
 #endif // OWLPS_LISTENER_USES_PTHREAD
 
@@ -772,7 +825,7 @@ int check_configuration()
         }
 
       if (GET_AUTOCALIBRATION_NBPKT() < 1)
-        fprintf(stderr, "Warning! autocalibration_nb_packets is null,"
+        fprintf(stderr, "Warning! autocalibration_nb_packets is zero,"
                 " no autocalibration request will be sent!\n") ;
 
       if (coordinates_provided)