diff --git a/compiler2/subtypestuff.hh b/compiler2/subtypestuff.hh
index bdf4b0f9ca12231df95218d3823a2d178b5d4742..b46dd797496db8aece6e1d109440b690761a217a 100644
--- a/compiler2/subtypestuff.hh
+++ b/compiler2/subtypestuff.hh
@@ -1786,7 +1786,7 @@ bool StringSubtypeTreeElement<STRINGTYPE,CHARLIMITTYPE>::is_element(const STRING
   default:
     FATAL_ERROR("StringSubtypeTreeElement::is_element()");
   }
-  return TUNKNOWN;
+  return true; // don't know if it matches
 }
 
 // if the constraints are ortogonal (e.g. size and alphabet) or just different then return TUNKNOWN