diff --git a/src/plugins/builtin/basic_blocks.ml b/src/plugins/builtin/basic_blocks.ml
index 7fcab6a2b79a2a0b047d5cb48e64326a6060ce15..1e2b50afa42c949ccf187a1c42d5faafd5aca2bc 100644
--- a/src/plugins/builtin/basic_blocks.ml
+++ b/src/plugins/builtin/basic_blocks.ml
@@ -210,13 +210,24 @@ and pall_elems_eq ?loc depth t1 value len =
   let tind = tvar ind in
   let bounds = pbounds_incl_excl ?loc (tinteger 0) tind len in
   let t1_acc = taccess ?loc t1 tind in
-  let eq = peq_unfold ?loc (depth+1) t1_acc value in
+  let eq = peq_unfold ?loc depth t1_acc value in
   pforall ?loc ([ind], (pimplies ?loc (bounds, eq)))
+and pall_fields_eq ?loc depth t1 ci value =
+  let eq fi =
+    let lval = match t1.term_node with TLval(lv) -> lv | _ -> assert false in
+    let nlval = addTermOffsetLval (TField(fi, TNoOffset)) lval in
+    let term = term ?loc (TLval nlval) (Ctype fi.ftype) in
+    peq_unfold ?loc depth term value
+  in
+  let eqs = List.map eq ci.cfields in
+  pands eqs
 and peq_unfold ?loc depth t1 value =
   match t1.term_type with
   | Ctype(TArray(_, Some len, _, _)) ->
     let len = Logic_utils.expr_to_term ~cast:false len in
-    pall_elems_eq ?loc depth t1 value len
+    pall_elems_eq ?loc (depth+1) t1 value len
+  | Ctype(TComp(ci, _, _)) ->
+    pall_fields_eq ?loc depth t1 ci value
   | _ -> prel ?loc (Req, t1, value)
 
 let pseparated_memories ?loc p1 len1 p2 len2 =
diff --git a/src/plugins/builtin/memset.ml b/src/plugins/builtin/memset.ml
index 1bd6ba655f72e44ac4b629570c984194918bf2a4..631a66bd4f318d3cf4d37d454972477593b81ab3 100644
--- a/src/plugins/builtin/memset.ml
+++ b/src/plugins/builtin/memset.ml
@@ -92,7 +92,9 @@ let generate_ensures e loc t ptr value len =
   let content = match e, value with
     | None, Some value ->
       [ { (pset_len_bytes ~loc ptr value len) with pred_name } ]
-    | Some 0, None -> []
+    | Some 0, None ->
+      let value = tinteger ~loc 0 in
+      [ { (pset_len_bytes ~loc ptr value len) with pred_name } ]
     | Some 255, None -> []
     | _ -> assert false
   in
@@ -128,8 +130,13 @@ let memset_value e =
   | Const(CInt64(ni, _, _)) when Integer.equal ni ff -> Some 255
   | _ -> None
 
+let is_union_type = function
+  | TComp({ cstruct = false }, _, _) -> true
+  | _ -> false
+
 let well_typed_call = function
   | [ ptr ; _ ; _ ] when any_char_composed_type (type_from_arg ptr) -> true
+  | [ ptr ; _ ; _ ] when is_union_type (type_from_arg ptr) -> false
   | [ _ ; value ; _ ] ->
     begin match memset_value value with
       | None -> false