diff --git a/fastfetch_server.c b/fastfetch_server.c
index 8c2f639..207f86b 100644
--- a/fastfetch_server.c
+++ b/fastfetch_server.c
@@ -172,6 +172,7 @@ int main(int argc, char *argv[]) {
         }
         else {
             port = atoi(argv[i]);
+            if (port <= 0) exit_error("unknown argument: %s\n", argv[i]);
         }
     }