diff --git a/frozen.h b/frozen.h
index 8473cfa..31aaff6 100644
--- a/frozen.h
+++ b/frozen.h
@@ -138,6 +138,7 @@ typedef int (*json_printf_callback_t)(struct json_out *, va_list *ap);
  * This is a superset of printf() function, with extra format specifiers:
  *  - `%B` print json boolean, `true` or `false`. Accepts an `int`.
  *  - `%Q` print quoted escaped string or `null`. Accepts a `const char *`.
+ *  - `%.*Q` same as `%Q`, but with length. Accepts `int`, `const char *`
  *  - `%V` print quoted base64-encoded string. Accepts a `const char *`, `int`.
  *  - `%M` invokes a json_printf_callback_t function. That callback function
  *  can consume more parameters.