diff --git a/gget.c b/gget.c
index 43ce4ca..49fab52 100644
--- a/gget.c
+++ b/gget.c
@@ -515,7 +515,12 @@ int main(int argc, char** argv)
     while ((opt = getopt(argc, argv, "hn:l:o:u:qm:")) != -1) {
         switch (opt) {
         case 'n':
-            nb_threads = atoi(optarg);
+            nb_threads = strtoul(optarg, &endptr, 0);
+            if (*endptr)
+            {
+                usage(argv[0]);
+                return 1;
+            }
             if (nb_threads == 0)
                 nb_threads = DEFAULT_NB_THREADS;
             else if (nb_threads > MAX_NB_THREADS)
@@ -525,7 +530,12 @@ int main(int argc, char** argv)
             }
             break;
         case 'l':
-            max_speed = atoi(optarg);
+            max_speed = strtoul(optarg, &endptr, 0);
+            if (*endptr)
+            {
+                usage(argv[0]);
+                return 1;
+            }
             break;
         case 'm':
             if (strlen(optarg) > 1)