diff --git a/.semgrep/let.yml b/.semgrep/let.yml
new file mode 100644
index 0000000000..f49e97d7e9
--- /dev/null
+++ b/.semgrep/let.yml
@@ -0,0 +1,6 @@
+rules:
+  - id: let-unit-in
+    pattern: let () = $E in ...
+    message: use ; instead (and, if needed, add surrounding parentheses to preserve precedence)
+    languages: [ocaml]
+    severity: WARNING
diff --git a/src/analyses/apron/apronAnalysis.apron.ml b/src/analyses/apron/apronAnalysis.apron.ml
index f4d72c3d71..5c449e63cf 100644
--- a/src/analyses/apron/apronAnalysis.apron.ml
+++ b/src/analyses/apron/apronAnalysis.apron.ml
@@ -36,7 +36,7 @@ let () =
   Printexc.register_printer
     (function
       | Apron.Manager.Error e ->
-        let () = Apron.Manager.print_exclog Format.str_formatter e in
-        Some(Printf.sprintf "Apron.Manager.Error\n %s" (Format.flush_str_formatter ()))
+        Apron.Manager.print_exclog Format.str_formatter e;
+        Some (Printf.sprintf "Apron.Manager.Error\n %s" (Format.flush_str_formatter ()))
       | _ -> None (* for other exceptions *)
     )
diff --git a/src/analyses/memOutOfBounds.ml b/src/analyses/memOutOfBounds.ml
index ff3946d047..72daac3a51 100644
--- a/src/analyses/memOutOfBounds.ml
+++ b/src/analyses/memOutOfBounds.ml
@@ -269,7 +269,7 @@ struct
           | None -> ID.bot_of @@ Cilfacade.ptrdiff_ikind ()
         end in
         let e_size = get_size_of_ptr_target man e in
-        let () = begin match e_size with
+        begin match e_size with
           | `Top ->
             (set_mem_safety_flag InvalidDeref;
              M.warn "Size of lval dereference expression %a is top. Out-of-bounds memory access may occur" d_exp e)
@@ -297,7 +297,7 @@ struct
                 (set_mem_safety_flag InvalidDeref;
                  M.warn ~category:(Behavior behavior) ~tags:[CWE cwe_number] "Could not compare size of lval dereference expression (%a) (in bytes) with offset by (%a) (in bytes). Memory out-of-bounds access might occur" ID.pretty casted_es ID.pretty casted_offs)
             end
-        end in
+        end;
         begin match e with
           | Lval (Var v, _) as lval_exp -> check_no_binop_deref man lval_exp
           | BinOp (binop, e1, e2, t) when binop = PlusPI || binop = MinusPI || binop = IndexPI ->
diff --git a/src/solver/sLRterm.ml b/src/solver/sLRterm.ml
index 947c73e4e1..7cde3e10ae 100644
--- a/src/solver/sLRterm.ml
+++ b/src/solver/sLRterm.ml
@@ -49,13 +49,13 @@ module SLR3term =
       let count  = ref 0 in
       let count_side  = ref (max_int - 1) in
 
-      let () = print_solver_stats := fun () ->
+      print_solver_stats := (fun () ->
           Logs.info "wpoint: %d, rho: %d, rho': %d, q: %d, count: %d, count_side: %d" (HM.length wpoint) (HM.length rho) (HPM.length rho') (H.size !q) (Int.neg !count) (max_int - !count_side);
           let histo = Hashtbl.create 13 in (* histogram: node id -> number of contexts *)
           HM.iter (fun k _ -> Hashtbl.modify_def 1 (S.Var.var_id k) ((+)1) histo) rho;
           let vid,n = Hashtbl.fold (fun k v (k',v') -> if v > v' then k,v else k',v') histo (Obj.magic (), 0) in
           Logs.info "max #contexts: %d for var_id %s" n vid
-      in
+        );
 
       let init ?(side=false) x =
         if not (HM.mem rho x) then begin
diff --git a/src/solver/td3.ml b/src/solver/td3.ml
index 69a5d8179d..71667eff9b 100644
--- a/src/solver/td3.ml
+++ b/src/solver/td3.ml
@@ -287,11 +287,11 @@ module Base =
         include WPS (EqS) (HM) (VS)
       end in
 
-      let () = print_solver_stats := fun () ->
+      print_solver_stats := (fun () ->
           print_data data;
           Logs.info "|called|=%d" (HM.length called);
           print_context_stats rho
-      in
+        );
 
       if GobConfig.get_bool "incremental.load" then (
         print_data_verbose data "Loaded data for incremental analysis";
diff --git a/src/solver/td_simplified.ml b/src/solver/td_simplified.ml
index 8844319e02..d2e8c93241 100644
--- a/src/solver/td_simplified.ml
+++ b/src/solver/td_simplified.ml
@@ -24,14 +24,14 @@ module Base : GenericEqSolver =
       let wpoint = HM.create 10 in
       let stable = HM.create 10 in
 
-      let () = print_solver_stats := fun () ->
+      print_solver_stats := (fun () ->
           Logs.debug "|rho|=%d" (HM.length rho);
           Logs.debug "|stable|=%d" (HM.length stable);
           Logs.debug "|infl|=%d" (HM.length infl);
           Logs.debug "|wpoint|=%d" (HM.length wpoint);
           Logs.info "|called|=%d" (HM.length called);
           print_context_stats rho
-      in
+        );
 
       let add_infl y x =
         if tracing then trace "infl" "add_infl %a %a" S.Var.pretty_trace y S.Var.pretty_trace x;
@@ -122,7 +122,7 @@ module Base : GenericEqSolver =
               if M.tracing then M.trace "wpoint" "widen %a" S.Var.pretty_trace x;
               box old eqd)
           in
-          if not (Timing.wrap "S.Dom.equal" (fun () -> S.Dom.equal old wpd) ()) then ( 
+          if not (Timing.wrap "S.Dom.equal" (fun () -> S.Dom.equal old wpd) ()) then (
             (* old != wpd *)
             if tracing && not (S.Dom.is_bot old) then trace "update" "%a (wpx: %b): %a" S.Var.pretty_trace x (HM.mem wpoint x) S.Dom.pretty_diff (wpd, old);
             update_var_event x old wpd;
@@ -132,7 +132,7 @@ module Base : GenericEqSolver =
             (iterate[@tailcall]) x
           ) else (
             (* old == wpd *)
-            if not (HM.mem stable x) then ( 
+            if not (HM.mem stable x) then (
               (* value unchanged, but not stable, i.e. destabilized itself during rhs *)
               if tracing then trace "iter" "iterate still unstable %a" S.Var.pretty_trace x;
               (iterate[@tailcall]) x
@@ -172,7 +172,7 @@ module Base : GenericEqSolver =
           );
           List.iter (fun x -> HM.replace called x ();
                       if tracing then trace "multivar" "solving for %a" S.Var.pretty_trace x;
-                      iterate x; 
+                      iterate x;
                       HM.remove called x
                     ) unstable_vs;
           solver ();
diff --git a/src/solver/td_simplified_ref.ml b/src/solver/td_simplified_ref.ml
index 76e8dde082..fb6f2182e9 100644
--- a/src/solver/td_simplified_ref.ml
+++ b/src/solver/td_simplified_ref.ml
@@ -28,9 +28,9 @@ module Base : GenericEqSolver =
     let solve st vs =
       let (data : var_data ref HM.t) = HM.create 10 in
 
-      let () = print_solver_stats := fun () ->
+      print_solver_stats := (fun () ->
           Logs.debug "|data|=%d" (HM.length data);
-      in
+        );
 
       let add_infl y x =
         if tracing then trace "infl" "add_infl %a %a" S.Var.pretty_trace y S.Var.pretty_trace x;
@@ -46,12 +46,12 @@ module Base : GenericEqSolver =
           begin
             new_var_event x;
             if tracing then trace "init" "init %a" S.Var.pretty_trace x;
-            let data_x = ref { 
+            let data_x = ref {
                 infl = VS.empty;
                 value = S.Dom.bot ();
                 wpoint = false;
                 stable = false;
-                called = false 
+                called = false
               } in
             HM.replace data x data_x;
             data_x
@@ -138,7 +138,7 @@ module Base : GenericEqSolver =
               if M.tracing then M.trace "wpoint" "widen %a" S.Var.pretty_trace x;
               box old eqd)
           in
-          if not (Timing.wrap "S.Dom.equal" (fun () -> S.Dom.equal old wpd) ()) then ( 
+          if not (Timing.wrap "S.Dom.equal" (fun () -> S.Dom.equal old wpd) ()) then (
             (* old != wpd *)
             if tracing && not (S.Dom.is_bot old) && !x_ref.wpoint then trace "solchange" "%a (wpx: %b): %a" S.Var.pretty_trace x (!x_ref.wpoint) S.Dom.pretty_diff (wpd, old);
             update_var_event x old wpd;
@@ -148,7 +148,7 @@ module Base : GenericEqSolver =
             (iterate[@tailcall]) x
           ) else (
             (* old == wpd *)
-            if not (!x_ref.stable) then ( 
+            if not (!x_ref.stable) then (
               (* value unchanged, but not stable, i.e. destabilized itself during rhs *)
               if tracing then trace "iter" "iterate still unstable %a" S.Var.pretty_trace x;
               (iterate[@tailcall]) x
@@ -185,12 +185,12 @@ module Base : GenericEqSolver =
             Logs.newline ();
             flush_all ();
           );
-          List.iter (fun x -> 
+          List.iter (fun x ->
               let x_ref = HM.find data x in
               x_ref := { !x_ref with called = true };
               if tracing then trace "multivar" "solving for %a" S.Var.pretty_trace x;
-              iterate x; 
-              x_ref := { !x_ref with called = false } 
+              iterate x;
+              x_ref := { !x_ref with called = false }
             ) unstable_vs;
           solver ();
         )