diff --git a/filter/filter.c b/filter/filter.c
index 81bfd4e5..bfb480ab 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -607,12 +607,6 @@ interpret(struct f_inst *what)
 	e = ea_find( (*f_rte)->attrs->eattrs, what->a2.i );
 
       if (!e) {
-	/* A special case: undefined int_set looks like empty int_set */
-	if ((what->aux & EAF_TYPE_MASK) == EAF_TYPE_INT_SET) {
-	  res.type = T_CLIST;
-	  res.val.ad = adata_empty(f_pool);
-	  break;
-	}
 	/* Undefined value */
 	res.type = T_VOID;
 	break;
@@ -821,7 +815,11 @@ interpret(struct f_inst *what)
 
   case P('C','a'):	/* Community list add or delete */
     TWOARGS;
-    if (v1.type != T_CLIST)
+
+    /* Replace undefined value with empty community list */ 
+    if (v1.type == T_VOID)
+      v1.val.ad = adata_empty(f_pool);
+    else if (v1.type != T_CLIST)
       runtime("Can't add/delete to non-clist");
     if (v2.type != T_PAIR)
       runtime("Can't add/delete non-pair");