diff --git a/ChangeLog.d/drbg-mutex.txt b/ChangeLog.d/drbg-mutex.txt
new file mode 100644
index 0000000..3ac5abf
--- /dev/null
+++ b/ChangeLog.d/drbg-mutex.txt
@@ -0,0 +1,5 @@
+Bugfix
+   * Fix a resource leak in CTR_DRBG and HMAC_DRBG when MBEDTLS_THREADING_C
+     is enabled, on platforms where initializing a mutex allocates resources.
+     This was a regression introduced in the previous release. Reported in
+     #4017, #4045 and #4071.