diff --git a/parse-options-cb.c b/parse-options-cb.c
index ba5acf3111..9f2f9b3df6 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -153,6 +153,18 @@ int parse_opt_noop_cb(const struct option *opt, const char *arg, int unset)
 	return 0;
 }
 
+/**
+ * Report that the option is unknown, so that other code can handle
+ * it. This can be used as a callback together with
+ * OPTION_LOWLEVEL_CALLBACK to allow an option to be documented in the
+ * "-h" output even if it's not being handled directly by
+ * parse_options().
+ */
+int parse_opt_unknown_cb(const struct option *opt, const char *arg, int unset)
+{
+	return -2;
+}
+
 /**
  * Recreates the command-line option in the strbuf.
  */
diff --git a/parse-options.h b/parse-options.h
index ea4af92a51..b2cc6a5574 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -228,6 +228,7 @@ extern int parse_opt_commits(const struct option *, const char *, int);
 extern int parse_opt_tertiary(const struct option *, const char *, int);
 extern int parse_opt_string_list(const struct option *, const char *, int);
 extern int parse_opt_noop_cb(const struct option *, const char *, int);
+extern int parse_opt_unknown_cb(const struct option *, const char *, int);
 extern int parse_opt_passthru(const struct option *, const char *, int);
 extern int parse_opt_passthru_argv(const struct option *, const char *, int);