diff --git a/modules/io/doc/mmcif.rst b/modules/io/doc/mmcif.rst
index c53a8b858d090bd3233170164482d40d50cbf1f9..f0ad0c7788c5d0faa585c0a2389fad07d3be61e3 100644
--- a/modules/io/doc/mmcif.rst
+++ b/modules/io/doc/mmcif.rst
@@ -245,7 +245,9 @@ of the annotation available.
   .. method:: GetMMCifPDBChainTr(cif_chain_id)
 
     Get the translation of a certain mmCIF chain name to the traditional PDB
-    chain name.
+    chain name. Only works if SEQRES records are read in
+    :func:`~ost.io.LoadMMCIF` and a compound library is available (see
+    :func:`~ost.conop.GetDefaultLib`).
 
     :param cif_chain_id: atom_site.label_asym_id
     :type cif_chain_id: :class:`str`