diff --git a/README.md b/README.md
index 91f99bc..c60477b 100644
--- a/README.md
+++ b/README.md
@@ -1017,6 +1017,7 @@ A 'catch-all' category for anything that doesn't fit well anywhere else.
   interface. [``BSD-3-Clause``][BSD-3-Clause]
 * [nope.c][209] - Ultra-light software platform for scalable server-side and
   networking applications (think node.js for C programmers). [``GPL-2.0-only``][GPL-2.0-only]
+* [ONLY_ONCE][552] - Like Rust's lazy_static, but for C. It's mt-safe, too! [``MIT``][MIT]
 * [parg][274] - A single-file reimplementation of ``getopt`` with better defaults.
   [``CC0-1.0``][CC0-1.0]
 * [pbc][236] - Protocol buffers library. [``MIT``][MIT]
@@ -1652,3 +1653,4 @@ support for C.
 [549]: https://github.com/LiamBindle/MQTT-C
 [550]: https://github.com/LeoVen/C-Macro-Collections
 [551]: https://github.com/mysql/mysql-server
+[552]: https://github.com/hexspeakerg/ONLY_ONCE