diff --git a/src/proto_alpha/lib_protocol/dal_slot_repr.ml b/src/proto_alpha/lib_protocol/dal_slot_repr.ml
index f467d706a2687d438365635484b5edc4a3c95184..515927adb8288aeae132e40fef7ada89e4a00a84 100644
--- a/src/proto_alpha/lib_protocol/dal_slot_repr.ml
+++ b/src/proto_alpha/lib_protocol/dal_slot_repr.ml
@@ -230,7 +230,7 @@ module History = struct
   end
 
   module Content_prefix = struct
-    let _prefix = "dash1"
+    let (_prefix : string) = "dash1"
 
     (* 32 *)
     let b58check_prefix = "\002\224\072\094\219" (* dash1(55) *)
@@ -248,7 +248,7 @@ module History = struct
   (* Pointers of the skip lists are used to encode the content and the
      backpointers. *)
   module Pointer_prefix = struct
-    let _prefix = "dask1"
+    let (_prefix : string) = "dask1"
 
     (* 32 *)
     let b58check_prefix = "\002\224\072\115\035" (* dask1(55) *)
diff --git a/src/proto_alpha/lib_protocol/merkle_list.ml b/src/proto_alpha/lib_protocol/merkle_list.ml
index 9f9aaa0c6da9d1629fa08e2d0137a5bd84fc93cf..bc41e7f1651a882aaabf5f205fb28f4c3209095e 100644
--- a/src/proto_alpha/lib_protocol/merkle_list.ml
+++ b/src/proto_alpha/lib_protocol/merkle_list.ml
@@ -31,7 +31,7 @@ let max_depth ~count_limit =
   let log2 n = Z.numbits (Z.of_int n) in
   log2 count_limit
 
-let _ =
+let () =
   register_error_kind
     `Temporary
     ~id:"Merkle_list_invalid_position"
diff --git a/src/proto_alpha/lib_protocol/sc_rollup_arith.ml b/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
index 2bf84893ec42a51b6ab7fc7cdbfc43cec875929f..2449001859ca19266ff70baa174addc8c6643f98 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_arith.ml
@@ -1047,7 +1047,7 @@ module Make (Context : P) :
   let parse : unit t =
     let open Monad.Syntax in
     let produce_add =
-      let* _ = lexeme in
+      let* (_ : string) = lexeme in
       let* () = next_char in
       let* () = Code.inject IAdd in
       return ()
@@ -1111,12 +1111,12 @@ module Make (Context : P) :
         | Some (' ' | '\n') -> next_char
         | Some '+' -> produce_add
         | Some d when is_digit d ->
-            let* _ = lexeme in
+            let* (_ : string) = lexeme in
             let* () = next_char in
             let* () = Parser_state.set ParseInt in
             return ()
         | Some d when is_letter d ->
-            let* _ = lexeme in
+            let* (_ : string) = lexeme in
             let* () = next_char in
             let* () = Parser_state.set ParseVar in
             return ()
diff --git a/src/proto_alpha/lib_protocol/sc_rollup_storage.ml b/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
index ec7e3384f17e3d1f9c93d049ee1bb39c98617a32..d6f35b9efccd147e60bf4740bc6ed8a01aa7bb5e 100644
--- a/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
+++ b/src/proto_alpha/lib_protocol/sc_rollup_storage.ml
@@ -225,9 +225,11 @@ module Dal_slot = struct
 
   let subscribe ctxt rollup ~slot_index =
     let open Lwt_tzresult_syntax in
-    let* _slot_index = fail_if_slot_index_invalid ctxt slot_index in
+    let* (_slot_index : Dal_slot_repr.Index.t) =
+      fail_if_slot_index_invalid ctxt slot_index
+    in
     (* Check if the rollup exists by looking for the initial level *)
-    let* _initial_level = genesis_info ctxt rollup in
+    let* ctxt, _initial_level = genesis_info ctxt rollup in
     let {Level_repr.level; _} = Raw_context.current_level ctxt in
     let* subscribed_slots = subscribed_slots_at_level ctxt rollup level in
     let*? slot_already_subscribed =
@@ -264,7 +266,7 @@ module Dal_slot = struct
     in
     let open Lwt_tzresult_syntax in
     (* Check if the rollup exists by looking for the initial level *)
-    let* _initial_level = genesis_info ctxt rollup in
+    let* ctxt, _initial_level = genesis_info ctxt rollup in
     let* subscribed_slots = subscribed_slots_at_level ctxt rollup level in
     let*? result = to_dal_slot_index_list subscribed_slots in
     return result
diff --git a/src/proto_alpha/lib_protocol/script_interpreter_defs.ml b/src/proto_alpha/lib_protocol/script_interpreter_defs.ml
index 08e3ef4451cccbfc265aadd2963be8ed718d93f1..0a87b0a382130b244414f0d7df82fa546bf88427 100644
--- a/src/proto_alpha/lib_protocol/script_interpreter_defs.ml
+++ b/src/proto_alpha/lib_protocol/script_interpreter_defs.ml
@@ -136,7 +136,7 @@ let cost_of_instr : type a s r f. (a, s, r, f) kinstr -> a -> s -> Gas.cost =
       let ss = accu in
       Interp_costs.concat_string_precheck ss
   | ISlice_string _ ->
-      let _offset = accu in
+      let (_offset : Script_int.n Script_int.num) = accu in
       let _length, (s, _) = stack in
       Interp_costs.slice_string s
   | IConcat_bytes_pair _ ->
@@ -353,7 +353,8 @@ let cost_of_instr : type a s r f. (a, s, r, f) kinstr -> a -> s -> Gas.cost =
   | ITicket _ | ITicket_deprecated _ -> Interp_costs.ticket
   | IRead_ticket _ -> Interp_costs.read_ticket
   | IOpen_chest _ ->
-      let _chest_key = accu and chest, (time, _) = stack in
+      let (_chest_key : Script_timelock.chest_key) = accu
+      and chest, (time, _) = stack in
       Interp_costs.open_chest ~chest ~time:(Script_int.to_zint time)
   | IEmit _ -> Interp_costs.emit
   | ILog _ -> Gas.free
diff --git a/src/proto_alpha/lib_protocol/script_interpreter_logging.ml b/src/proto_alpha/lib_protocol/script_interpreter_logging.ml
index d09762eca53a06d5d9763f878460fc2fb9fc0dea..4822a9d5fb267e31dc38afb6ed2bc0e29ddb529e 100644
--- a/src/proto_alpha/lib_protocol/script_interpreter_logging.ml
+++ b/src/proto_alpha/lib_protocol/script_interpreter_logging.ml
@@ -1737,7 +1737,6 @@ let log_entry logger ctxt gas k sty accu stack =
   logger.log_entry k ctxt (kinstr_location k) sty (accu, stack)
 
 let log_exit logger ctxt gas loc_prev k sty accu stack =
-  let _loc = kinstr_location k in
   let ctxt = Local_gas_counter.update_context gas ctxt in
   logger.log_exit k ctxt loc_prev sty (accu, stack)