diff --git a/src/SMESH_I/SMESH_Filter_i.cxx b/src/SMESH_I/SMESH_Filter_i.cxx
index f2ce323ed..b7c9c8ffb 100644
--- a/src/SMESH_I/SMESH_Filter_i.cxx
+++ b/src/SMESH_I/SMESH_Filter_i.cxx
@@ -3792,7 +3792,7 @@ static const char** getFunctNames()
 const char* SMESH::FunctorTypeToString(SMESH::FunctorType ft)
 {
   if ( ft < 0 || ft > SMESH::FT_Undefined )
-    return 0;
+    return "FT_Undefined";
   return getFunctNames()[ ft ];
 }