diff --git a/src/igmpgen.c b/src/igmpgen.c
index 21b4041..dde87e7 100644
--- a/src/igmpgen.c
+++ b/src/igmpgen.c
@@ -151,6 +151,10 @@ int main(int argc, char **argv)
                 ip_src_str = strdup(optarg);
                 printf("  Source = ip [%s] port [%d]\n", ip_src_str, src_prt);
                 break;
+
+            default:
+                usage(argv[0]);
+                exit(1);
         }
     }
     if (!igmp_group_str || !device)