diff --git a/parse-options.h b/parse-options.h
index 98ea42f..ac6ba8a 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -292,7 +292,9 @@
 int parse_opt_tertiary(const struct option *, const char *, int);
 int parse_opt_string_list(const struct option *, const char *, int);
 int parse_opt_noop_cb(const struct option *, const char *, int);
-int parse_opt_unknown_cb(struct parse_opt_ctx_t *ctx, const struct option *, const char *, int);
+enum parse_opt_result parse_opt_unknown_cb(struct parse_opt_ctx_t *ctx,
+					   const struct option *,
+					   const char *, int);
 int parse_opt_passthru(const struct option *, const char *, int);
 int parse_opt_passthru_argv(const struct option *, const char *, int);