diff --git a/deploy/gen_runtime_config.php b/deploy/gen_runtime_config.php
index f2ea0e3..f8bb5d4 100755
--- a/deploy/gen_runtime_config.php
+++ b/deploy/gen_runtime_config.php
@@ -50,7 +50,7 @@ function usage(string $msg = ''): never  {
     if ($msg !== '')
         fwrite(STDERR, "error: {$msg}\n");
     $script = $GLOBALS['argv'][0];
-    fwrite(STDERR, "usage: {$script} --htdocs_dir DIR --commit-hash HASH\n");
+    fwrite(STDERR, "usage: {$script} --htdocs-dir DIR --commit-hash HASH\n");
     exit(1);
 }