diff --git a/filter/f-inst.c b/filter/f-inst.c
index 0867ac4a..49ae993a 100644
--- a/filter/f-inst.c
+++ b/filter/f-inst.c
@@ -308,12 +308,24 @@
 	case T_PATH_MASK_ITEM:
 	  pm->item[i] = vv(i).val.pmi;
 	  break;
+
 	case T_INT:
 	  pm->item[i] = (struct f_path_mask_item) {
 	    .asn = vv(i).val.i,
 	    .kind = PM_ASN,
 	  };
 	  break;
+
+	case T_SET:
+	  if (vv(i).val.t->from.type != T_INT)
+	    runtime("Only integer sets allowed in path mask");
+
+	  pm->item[i] = (struct f_path_mask_item) {
+	    .set = vv(i).val.t,
+	    .kind = PM_ASN_SET,
+	  };
+	  break;
+
 	default:
 	  runtime( "Error resolving path mask template: value not an integer" );
       }
diff --git a/filter/test.conf b/filter/test.conf
index 04074965..09a4a88a 100644
--- a/filter/test.conf
+++ b/filter/test.conf
@@ -597,11 +597,15 @@ function mkpath(int a; int b)
 	return [= a b 3 2 1 =];
 }
 
+define set35 = [3 .. 5];
+
 function t_path()
 bgpmask pm1;
 bgppath p2;
+int set set12;
 {
 	pm1 = [= 4 3 2 1 =];
+	set12 = [1, 2];
 
 	bt_assert(format(pm1) = "[= 4 3 2 1 =]");
 
@@ -627,6 +631,7 @@ bgppath p2;
 	bt_assert(p2 ~ [= * 4 3 * 1 =]);
 	bt_assert(p2 ~ [= (3+2) (2*2) 3 2 1 =]);
 	bt_assert(p2 ~ [= 5 [2, 4, 6] 3 [1..2] 1 =]);
+	bt_assert(p2 ~ [= 5 set35 3 set12 set12 =]);
 	bt_assert(p2 ~ mkpath(5, 4));
 
 	bt_assert(p2.len = 5);
diff --git a/nest/a-path.c b/nest/a-path.c
index 4ee34cf4..b6a30f54 100644
--- a/nest/a-path.c
+++ b/nest/a-path.c
@@ -741,7 +741,7 @@ pm_match(struct pm_pos *pos, u32 asn, u32 asn2)
 }
 
 static int
-pm_match_set(struct pm_pos *pos, struct f_tree *set)
+pm_match_set(struct pm_pos *pos, const struct f_tree *set)
 {
   struct f_val asn = { .type = T_INT };
 
diff --git a/nest/attrs.h b/nest/attrs.h
index a17b8c05..6fb0a8fa 100644
--- a/nest/attrs.h
+++ b/nest/attrs.h
@@ -65,8 +65,8 @@ static inline struct adata *as_path_prepend(struct linpool *pool, const struct a
 struct f_path_mask_item {
   union {
     u32 asn; /* PM_ASN */
-    struct f_line *expr; /* PM_ASN_EXPR */
-    struct f_tree *set; /* PM_ASN_SET */
+    const struct f_line *expr; /* PM_ASN_EXPR */
+    const struct f_tree *set; /* PM_ASN_SET */
     struct { /* PM_ASN_RANGE */
       u32 from;
       u32 to;