diff --git a/src/stdio-bridge/stdio-bridge.c b/src/stdio-bridge/stdio-bridge.c
index f48b7e574e..71326789cb 100644
--- a/src/stdio-bridge/stdio-bridge.c
+++ b/src/stdio-bridge/stdio-bridge.c
@@ -92,10 +92,14 @@ static int parse_argv(int argc, char *argv[]) {
                         return -EINVAL;
 
                 default:
-                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
-                                               "Unknown option code %c", c);
+                        assert_not_reached();
                 }
 
+        if (argc > optind)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "%s takes no arguments.",
+                                       program_invocation_short_name);
+
         return 1;
 }