diff --git a/src/abstract/Extend.gf b/src/abstract/Extend.gf
index 8ba3ad41..e58043ef 100644
--- a/src/abstract/Extend.gf
+++ b/src/abstract/Extend.gf
@@ -287,4 +287,6 @@ fun UseDAP     : DAP -> NP ;
     UseDAPMasc : DAP -> NP ;
     UseDAPFem  : DAP -> NP ;
 
+cat X ; -- for words that are difficult to classify, mainly for MorphoDict
+
 }
diff --git a/src/common/ExtendFunctor.gf b/src/common/ExtendFunctor.gf
index 51785c2d..1906fa57 100644
--- a/src/common/ExtendFunctor.gf
+++ b/src/common/ExtendFunctor.gf
@@ -4,6 +4,8 @@ lincat
   RNP = Grammar.NP ;
   RNPList = Grammar.ListNP ;
 
+  X = {s : Str} ; -- for words that are difficult to classify, mainly for MorphoDict
+
 lin
   BaseVPS = variants {} ;
   ConsVPS = variants {} ;