diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 489802cbc8d..f164b3baf72 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -614,6 +614,15 @@ Bug Fixes since HDF5-1.14.3 release
       of MPI-2 maintenance and testing since version HDF5 1.12.
 
 
+    - Fixed a segfault when using a user-defined conversion function between compound datatypes
+
+      During type info initialization for compound datatype conversion, the library checked if the
+      datatypes are subsets of one another in order to perform special conversion handling. 
+      This check uses information that is only defined if a library conversion function is in use. 
+      The library now skips this check for user-defined conversion functions.
+
+      Fixes Github issue #3840
+
     Java Library
     ------------
     -