diff --git a/src/smt/preprocess.ml b/src/smt/preprocess.ml
index be3f51a4..91c080dd 100644
--- a/src/smt/preprocess.ml
+++ b/src/smt/preprocess.ml
@@ -10,12 +10,6 @@ end
 
 type preprocess_actions = (module PREPROCESS_ACTS)
 
-(* action taken later *)
-type delayed_action =
-  | DA_add_clause of lit list * step_id
-  | DA_add_lit of { default_pol: bool option; lit: lit }
-  | DA_declare_need_th_combination of term
-
 type t = {
   tst: Term.store;  (** state for managing terms *)
   cc: CC.t;
@@ -23,7 +17,6 @@ type t = {
   proof: proof_trace;
   mutable preprocess: preprocess_hook list;
   preprocessed: Term.t Term.Tbl.t;
-  delayed_actions: delayed_action Vec.t;
   n_preprocess_clause: int Stat.counter;
 }
 
@@ -43,40 +36,14 @@ let create ?(stat = Stat.global) ~proof ~cc ~simplify tst : t =
     simplify;
     preprocess = [];
     preprocessed = Term.Tbl.create 8;
-    delayed_actions = Vec.create ();
     n_preprocess_clause = Stat.mk_int stat "smt.preprocess.n-clauses";
   }
 
 let on_preprocess self f = self.preprocess <- f :: self.preprocess
 let cc self = self.cc
 
-let pop_delayed_actions self =
-  if Vec.is_empty self.delayed_actions then
-    Iter.empty
-  else (
-    let a = Vec.to_array self.delayed_actions in
-    Vec.clear self.delayed_actions;
-    Iter.of_array a
-  )
-
-let declare_need_th_combination (self : t) (t : term) : unit =
-  Vec.push self.delayed_actions (DA_declare_need_th_combination t)
-
-let preprocess_term_ (self : t) (t : term) : term =
-  let module A = struct
-    let proof = self.proof
-    let mk_lit ?sign t : Lit.t = Lit.atom ?sign self.tst t
-
-    let add_lit ?default_pol lit : unit =
-      Vec.push self.delayed_actions (DA_add_lit { default_pol; lit })
-
-    let add_clause c pr : unit =
-      Vec.push self.delayed_actions (DA_add_clause (c, pr))
-
-    let declare_need_th_combination t = declare_need_th_combination self t
-  end in
-  let acts = (module A : PREPROCESS_ACTS) in
-
+let preprocess_term_ (self : t) ((module A : PREPROCESS_ACTS) as acts)
+    (t : term) : term =
   (* how to preprocess a term and its subterms *)
   let rec preproc_rec_ ~is_sub t0 : Term.t =
     match Term.Tbl.find_opt self.preprocessed t0 with
@@ -137,7 +104,8 @@ let preprocess_term_ (self : t) (t : term) : term =
 (* preprocess the literal. The result must be logically equivalent;
    as a rule of thumb, it should be the same term inside except with
    some [box] added whenever a theory frontier is crossed. *)
-let simplify_and_preproc_lit (self : t) (lit : Lit.t) : Lit.t * step_id option =
+let simplify_and_preproc_lit (self : t) acts (lit : Lit.t) :
+    Lit.t * step_id option =
   let t = Lit.term lit in
   let sign = Lit.sign lit in
 
@@ -150,7 +118,7 @@ let simplify_and_preproc_lit (self : t) (lit : Lit.t) : Lit.t * step_id option =
             Term.pp_debug u);
       u, Some pr_t_u
   in
-  let v = preprocess_term_ self u in
+  let v = preprocess_term_ self acts u in
   Lit.atom ~sign self.tst v, pr
 
 module type ARR = sig
@@ -163,12 +131,12 @@ end
 module Preprocess_clause (A : ARR) = struct
   (* preprocess a clause's literals, possibly emitting a proof
      for the preprocessing. *)
-  let top (self : t) (c : lit A.t) (pr_c : step_id) : lit A.t * step_id =
+  let top (self : t) acts (c : lit A.t) (pr_c : step_id) : lit A.t * step_id =
     let steps = ref [] in
 
     (* simplify a literal, then preprocess it *)
     let[@inline] simp_lit lit =
-      let lit, pr = simplify_and_preproc_lit self lit in
+      let lit, pr = simplify_and_preproc_lit self acts lit in
       Option.iter (fun pr -> steps := pr :: !steps) pr;
       lit
     in
diff --git a/src/smt/preprocess.mli b/src/smt/preprocess.mli
index 1f448a4f..b0aad86f 100644
--- a/src/smt/preprocess.mli
+++ b/src/smt/preprocess.mli
@@ -59,18 +59,13 @@ type preprocess_hook =
 val on_preprocess : t -> preprocess_hook -> unit
 (** Add a hook that will be called when terms are preprocessed *)
 
-val simplify_and_preproc_lit : t -> lit -> lit * step_id option
-val preprocess_clause : t -> lit list -> step_id -> lit list * step_id
-val preprocess_clause_array : t -> lit array -> step_id -> lit array * step_id
+val simplify_and_preproc_lit :
+  t -> preprocess_actions -> lit -> lit * step_id option
+
+val preprocess_clause :
+  t -> preprocess_actions -> lit list -> step_id -> lit list * step_id
+
+val preprocess_clause_array :
+  t -> preprocess_actions -> lit array -> step_id -> lit array * step_id
+
 val cc : t -> CC.t
-
-(** {2 Delayed actions} *)
-
-(** Action that preprocess hooks took, but were not effected yet.
-    The SMT solver itself should obtain these actions and perform them. *)
-type delayed_action =
-  | DA_add_clause of lit list * step_id
-  | DA_add_lit of { default_pol: bool option; lit: lit }
-  | DA_declare_need_th_combination of term
-
-val pop_delayed_actions : t -> delayed_action Iter.t
diff --git a/src/smt/solver_internal.ml b/src/smt/solver_internal.ml
index a337f3c7..891efd61 100644
--- a/src/smt/solver_internal.ml
+++ b/src/smt/solver_internal.ml
@@ -121,18 +121,24 @@ let delayed_add_lit (self : t) ?default_pol (lit : Lit.t) : unit =
 let delayed_add_clause (self : t) ~keep (c : Lit.t list) (pr : step_id) : unit =
   Queue.push (DA_add_clause { c; pr; keep }) self.delayed_actions
 
-let add_preprocess_delayed_actions (self : t) : unit =
-  Preprocess.pop_delayed_actions self.preprocess (function
-    | DA_add_clause (c, pr) -> delayed_add_clause self ~keep:true c pr
-    | DA_add_lit { default_pol; lit } -> delayed_add_lit self ?default_pol lit
-    | DA_declare_need_th_combination t ->
-      Th_combination.add_term_needing_combination self.th_comb t)
+let preprocess_acts (self : t) : Preprocess.preprocess_actions =
+  (module struct
+    let proof = self.proof
+    let mk_lit ?sign t : Lit.t = Lit.atom ?sign self.tst t
+    let add_clause c pr = delayed_add_clause self ~keep:true c pr
+    let add_lit ?default_pol lit = delayed_add_lit self ?default_pol lit
+
+    let declare_need_th_combination t =
+      Th_combination.add_term_needing_combination self.th_comb t
+  end)
 
 let push_decision (self : t) (acts : theory_actions) (lit : lit) : unit =
   let (module A) = acts in
   (* make sure the literal is preprocessed *)
-  let lit, _ = Preprocess.simplify_and_preproc_lit self.preprocess lit in
-  add_preprocess_delayed_actions self;
+  let lit, _ =
+    Preprocess.simplify_and_preproc_lit self.preprocess (preprocess_acts self)
+      lit
+  in
   let sign = Lit.sign lit in
   A.add_decision_lit (Lit.abs lit) sign
 
@@ -150,12 +156,16 @@ module Perform_delayed (A : PERFORM_ACTS) = struct
       let act = Queue.pop self.delayed_actions in
       match act with
       | DA_add_clause { c; pr = pr_c; keep } ->
-        let c', pr_c' = Preprocess.preprocess_clause self.preprocess c pr_c in
-        add_preprocess_delayed_actions self;
+        let c', pr_c' =
+          Preprocess.preprocess_clause self.preprocess (preprocess_acts self) c
+            pr_c
+        in
         A.add_clause self acts ~keep c' pr_c'
       | DA_add_lit { default_pol; lit } ->
-        let lit, _ = Preprocess.simplify_and_preproc_lit self.preprocess lit in
-        add_preprocess_delayed_actions self;
+        let lit, _ =
+          Preprocess.simplify_and_preproc_lit self.preprocess
+            (preprocess_acts self) lit
+        in
         A.add_lit self acts ?default_pol lit
     done
 end
@@ -174,28 +184,24 @@ end)
 let[@inline] preprocess self = self.preprocess
 
 let preprocess_clause self c pr =
-  let r = Preprocess.preprocess_clause self.preprocess c pr in
-  add_preprocess_delayed_actions self;
-  r
+  Preprocess.preprocess_clause self.preprocess (preprocess_acts self) c pr
 
 let preprocess_clause_array self c pr =
-  let r = Preprocess.preprocess_clause_array self.preprocess c pr in
-  add_preprocess_delayed_actions self;
-  r
+  Preprocess.preprocess_clause_array self.preprocess (preprocess_acts self) c pr
 
 let simplify_and_preproc_lit self lit =
-  let r = Preprocess.simplify_and_preproc_lit self.preprocess lit in
-  add_preprocess_delayed_actions self;
-  r
+  Preprocess.simplify_and_preproc_lit self.preprocess (preprocess_acts self) lit
 
 let[@inline] add_clause_temp self _acts c (proof : step_id) : unit =
-  let c, proof = Preprocess.preprocess_clause self.preprocess c proof in
-  add_preprocess_delayed_actions self;
+  let c, proof =
+    Preprocess.preprocess_clause self.preprocess (preprocess_acts self) c proof
+  in
   delayed_add_clause self ~keep:false c proof
 
 let[@inline] add_clause_permanent self _acts c (proof : step_id) : unit =
-  let c, proof = Preprocess.preprocess_clause self.preprocess c proof in
-  add_preprocess_delayed_actions self;
+  let c, proof =
+    Preprocess.preprocess_clause self.preprocess (preprocess_acts self) c proof
+  in
   delayed_add_clause self ~keep:true c proof
 
 let[@inline] mk_lit self ?sign t : lit = Lit.atom ?sign self.tst t
@@ -211,8 +217,10 @@ let[@inline] add_lit self _acts ?default_pol lit =
 
 let add_lit_t self _acts ?sign t =
   let lit = Lit.atom ?sign self.tst t in
-  let lit, _ = Preprocess.simplify_and_preproc_lit self.preprocess lit in
-  add_preprocess_delayed_actions self;
+  let lit, _ =
+    Preprocess.simplify_and_preproc_lit self.preprocess (preprocess_acts self)
+      lit
+  in
   delayed_add_lit self lit
 
 let on_final_check self f = self.on_final_check <- f :: self.on_final_check