diff --git a/modules/mol/base/src/chain_type.cc b/modules/mol/base/src/chain_type.cc
index 0820407c7b70821a42444cfb3dc6b0c9f97690fc..8b1c444bc8dd831f2b57fd51bf1c7568c3f3516e 100644
--- a/modules/mol/base/src/chain_type.cc
+++ b/modules/mol/base/src/chain_type.cc
@@ -78,6 +78,8 @@ String StringFromChainType(ChainType type)
 {
   // chain types as found in the entity category of a mmcif file
   if (CHAINTYPE_POLY == type) {
+    // "polymer" in _entity.type
+    // "other" in _entity_poly.type
     return "polymer";
   } else if (CHAINTYPE_NON_POLY == type) {
     return "non-polymer";
diff --git a/modules/mol/base/src/chain_type.hh b/modules/mol/base/src/chain_type.hh
index 27e1910e61bdd58bbf98df8d6d28bf4042d48744..f062606ec9e11d1544e04910ec10cc822be5ce8c 100644
--- a/modules/mol/base/src/chain_type.hh
+++ b/modules/mol/base/src/chain_type.hh
@@ -30,8 +30,8 @@ namespace ost { namespace mol {
 /// \enum different kinds of chains
 ///
 /// Warning: this class mixes vocabulary from _entity.type and
-// _entity_poly.type, which is more detailed. As a result it cannot be used to
-/// to read/write mmCIF entity types accurately.
+// _entity_poly.type, which is more detailed. As a result it is not a 1:1
+// mapping and cannot be used to to read/write mmCIF entity types accurately.
 
 typedef enum {
   CHAINTYPE_POLY,           ///< polymer