diff --git a/src/smt/model_builder.ml b/src/smt/model_builder.ml
index 2b07f902..4905fed4 100644
--- a/src/smt/model_builder.ml
+++ b/src/smt/model_builder.ml
@@ -5,7 +5,7 @@ module TM = Term.Map
 type t = {
   tst: Term.store;
   mutable m: Term.t TM.t;
-  required: Term.t Queue.t;
+  required: (Term.t * Term.t Iter.t) Queue.t;
   gensym: Gensym.t;
 }
 
@@ -18,25 +18,19 @@ let pp out (self : t) : unit =
   in
   Fmt.fprintf out "(@[model-builder@ :model %a@ :q (@[%a@])@])"
     (Util.pp_iter pp_kv) (TM.to_iter self.m) (Util.pp_iter T.pp)
-    (Iter.of_queue self.required)
+    (Iter.of_queue self.required |> Iter.map fst)
 
 let gensym self ~pre ~ty : Term.t = Gensym.fresh_term self.gensym ~pre ty
 
-let rec pop_required (self : t) : _ option =
-  match Queue.take_opt self.required with
-  | None -> None
-  | Some t when TM.mem t self.m -> pop_required self
-  | Some t -> Some t
-
-let require_eval (self : t) t : unit =
-  if not @@ TM.mem t self.m then Queue.push t self.required
+let require_eval (self : t) t ~cls : unit =
+  if not @@ TM.mem t self.m then Queue.push (t, cls) self.required
 
 let[@inline] mem self t : bool = TM.mem t self.m
 
 let add (self : t) ?(subs = []) t v : unit =
   if not @@ mem self t then (
     self.m <- TM.add t v self.m;
-    List.iter (fun u -> require_eval self u) subs
+    List.iter (fun u -> require_eval self u ~cls:Iter.empty) subs
   )
 
 type eval_cache = Term.Internal_.cache
@@ -56,6 +50,15 @@ let eval ?(cache = Term.Internal_.create_cache 8) (self : t) (t : Term.t) =
   T.Internal_.replace_ ~cache self.tst ~recursive:true t ~f:(fun ~recurse:_ u ->
       TM.get u self.m)
 
+let rec pop_required (self : t) : _ option =
+  match Queue.take_opt self.required with
+  | None -> None
+  | Some (t, cls) when TM.mem t self.m ->
+    (* make sure we also map [cls] to [t]'s value *)
+    cls (fun u -> add self u (TM.find t self.m));
+    pop_required self
+  | Some pair -> Some pair
+
 let to_map ?(cache = T.Internal_.create_cache 8) (self : t) : _ TM.t =
   (* ensure we evaluate each term only once by using a cache *)
   let map =
diff --git a/src/smt/model_builder.mli b/src/smt/model_builder.mli
index 23948711..0934d4d1 100644
--- a/src/smt/model_builder.mli
+++ b/src/smt/model_builder.mli
@@ -15,8 +15,9 @@ include Sidekick_sigs.PRINT with type t := t
 val create : Term.store -> t
 val mem : t -> Term.t -> bool
 
-val require_eval : t -> Term.t -> unit
-(** Require that this term gets a value. *)
+val require_eval : t -> Term.t -> cls:Term.t Iter.t -> unit
+(** Require that this term gets a value, and assign it to all terms
+  in the given class. *)
 
 val add : t -> ?subs:Term.t list -> Term.t -> value -> unit
 (** Add a value to the model.
@@ -32,7 +33,7 @@ val create_cache : int -> eval_cache
 val eval : ?cache:eval_cache -> t -> Term.t -> value
 val eval_opt : ?cache:eval_cache -> t -> Term.t -> value option
 
-val pop_required : t -> Term.t option
+val pop_required : t -> (Term.t * Term.t Iter.t) option
 (** gives the next subterm that is required but has no value yet *)
 
 val to_map : ?cache:eval_cache -> t -> value Term.Map.t
diff --git a/src/smt/solver_internal.ml b/src/smt/solver_internal.ml
index bf5bfff1..fc2326d1 100644
--- a/src/smt/solver_internal.ml
+++ b/src/smt/solver_internal.ml
@@ -360,39 +360,44 @@ let mk_model_ (self : t) (lits : lit Iter.t) : Model.t =
 
   (* require a value for each class that doesn't already have one *)
   CC.all_classes cc (fun repr ->
+      Log.debugf 5 (fun k ->
+          k "(@[model.fixpoint.require-cls@ %a@])" E_node.pp repr);
       let t = E_node.term repr in
-      MB.require_eval model t);
+      let ts = E_node.iter_class repr |> Iter.map E_node.term in
+      MB.require_eval model t ~cls:ts);
 
   (* now for the fixpoint. This is typically where composite theories such
      as arrays and datatypes contribute their skeleton values. *)
-  let rec compute_fixpoint () =
-    match MB.pop_required model with
-    | None -> ()
-    | Some t when Term.is_pi (Term.ty t) ->
-      (* TODO: when we support lambdas? *)
-      ()
-    | Some t ->
-      (* compute a value for [t] *)
-      Log.debugf 5 (fun k ->
-          k "(@[model.fixpoint.compute-for-required@ %a@])" Term.pp t);
+  let compute_fixpoint () =
+    let continue = ref true in
+    while !continue do
+      match MB.pop_required model with
+      | None -> continue := false
+      | Some (t, _cls) when Term.is_pi (Term.ty t) ->
+        (* TODO: when we support lambdas? *)
+        ()
+      | Some (t, cls) ->
+        (* compute a value for [t] *)
+        Log.debugf 5 (fun k ->
+            k "(@[model.fixpoint.compute-for-required@ %a@])" Term.pp t);
 
-      (* try each model hook *)
-      let rec try_hooks_ = function
-        | [] ->
-          (* should not happen *)
-          Error.errorf "cannot build a value for term@ `%a`@ of type `%a`"
-            Term.pp t Term.pp (Term.ty t)
-        | h :: hooks ->
-          (match h self model t with
-          | None -> try_hooks_ hooks
-          | Some (v, subs) ->
-            MB.add model ~subs t v;
-            ())
-      in
+        (* try each model hook *)
+        let rec try_hooks_ = function
+          | h :: hooks ->
+            (match h self model t with
+            | None -> try_hooks_ hooks
+            | Some (v, subs) ->
+              MB.add model ~subs t v;
+              cls (fun u -> MB.add model ~subs:[] u v);
+              ())
+          | [] ->
+            (* should not happen *)
+            Error.errorf "cannot build a value for term@ `%a`@ of type `%a`"
+              Term.pp t Term.pp (Term.ty t)
+        in
 
-      try_hooks_ model_ask_hooks;
-      (* continue to next value *)
-      (compute_fixpoint [@tailcall]) ()
+        try_hooks_ model_ask_hooks
+    done
   in
 
   compute_fixpoint ();
@@ -402,7 +407,7 @@ let mk_model_ (self : t) (lits : lit Iter.t) : Model.t =
   let eval (t : Term.t) : value option =
     try Some (Term.Map.find t map)
     with Not_found ->
-      MB.require_eval model t;
+      MB.require_eval model t ~cls:Iter.empty;
       compute_fixpoint ();
       MB.eval_opt ~cache model t
   in