diff --git a/source/sign.c b/source/sign.c
index c042d23..1225192 100644
--- a/source/sign.c
+++ b/source/sign.c
@@ -48,7 +48,7 @@ static int parse_args(struct args *args, int argc, char *argv[])
 		case OPTION_DIGEST: args->digest = optarg; break;
 		case OPTION_KEY: args->key = optarg; break;
 		case OPTION_CERT: args->cert = optarg; break;
-		default: break;
+		default: return -1;
 		}
 	}
 
diff --git a/source/verify.c b/source/verify.c
index 75c86f2..4d750df 100644
--- a/source/verify.c
+++ b/source/verify.c
@@ -44,7 +44,7 @@ static int parse_args(struct args *args, int argc, char *argv[])
 		case OPTION_HELP: return -1;
 		case OPTION_IMAGE: args->image = optarg; break;
 		case OPTION_CERTS: args->certs = optarg; break;
-		default: break;
+		default: return -1;
 		}
 	}