diff --git a/ChangeLog.d/issue4128.txt b/ChangeLog.d/issue4128.txt
new file mode 100644
index 0000000000..421740397d
--- /dev/null
+++ b/ChangeLog.d/issue4128.txt
@@ -0,0 +1,4 @@
+API changes
+   * The option `MBEDTLS_ECP_FIXED_POINT_OPTIM` use pre-computed comb tables
+     instead of computing tables in runtime. Thus, this option now use more
+     ROM, and it does not increase RAM usage in runtime anymore.
diff --git a/docs/3.0-migration-guide.d/modify_MBEDTLS_ECP_FIXED_POINT_OPTIM_behaviour.md b/docs/3.0-migration-guide.d/modify_MBEDTLS_ECP_FIXED_POINT_OPTIM_behaviour.md
new file mode 100644
index 0000000000..02a083c44b
--- /dev/null
+++ b/docs/3.0-migration-guide.d/modify_MBEDTLS_ECP_FIXED_POINT_OPTIM_behaviour.md
@@ -0,0 +1,8 @@
+Change MBEDTLS_ECP_FIXED_POINT_OPTIM behaviour
+------------------------------------------------------
+
+The option MBEDTLS_ECP_FIXED_POINT_OPTIM now use more ROM and does not increase
+peak RAM usage anymore.
+
+If you are limited by ROM space, you can define MBEDTLS_ECP_FIXED_POINT_OPTIM
+to `0` in your config file. This will save about 50 KiB ROM space.