diff --git a/src/dune_pkg/diagnostics.ml b/src/dune_pkg/diagnostics.ml
index 590859241c7..1c1c231d4d5 100644
--- a/src/dune_pkg/diagnostics.ml
+++ b/src/dune_pkg/diagnostics.ml
@@ -277,7 +277,7 @@ module Make (Results : S.SOLVER_RESULT) = struct
 
   type t = Component.t RoleMap.t
 
-  let find_component_ex role report =
+  let[@ocaml.warning "-32"] find_component_ex role report =
     match RoleMap.find report role with
     | Some c -> c
     | None ->
diff --git a/src/dune_pkg/zeroinstall_solver.mli b/src/dune_pkg/diagnostics.mli
similarity index 79%
rename from src/dune_pkg/zeroinstall_solver.mli
rename to src/dune_pkg/diagnostics.mli
index 220e251d867..d542511faba 100644
--- a/src/dune_pkg/zeroinstall_solver.mli
+++ b/src/dune_pkg/diagnostics.mli
@@ -1,26 +1,8 @@
 (* Copyright (C) 2020, Thomas Leonard
    See the README file for details, or visit http://0install.net. *)
 
-module S = S
-
-(** Select a compatible set of components to run a program.
-    See [Zeroinstall.Solver] for the instantiation of this functor on the
-    actual 0install types. *)
-module Make (Input : S.SOLVER_INPUT) : sig
-  module Output : S.SOLVER_RESULT with module Input = Input
-
-  (** [do_solve model req] finds an implementation matching the given requirements, plus any other implementations needed
-      to satisfy its dependencies.
-      @param closest_match
-        adds a lowest-ranked (but valid) implementation ([Input.dummy_impl]) to
-        every interface, so we can always select something. Useful for diagnostics.
-        Note: always try without [closest_match] first, or it may miss a valid solution.
-      @return None if the solve fails (only happens if [closest_match] is false). *)
-  val do_solve : closest_match:bool -> Input.Role.t -> Output.t option Fiber.t
-end
-
 (** Explaining why a solve failed or gave an unexpected answer. *)
-module Diagnostics (Result : S.SOLVER_RESULT) : sig
+module Make (Result : S.SOLVER_RESULT) : sig
   (** An item of information to display for a component. *)
   module Note : sig
     type t =
diff --git a/src/dune_pkg/opam_solver.ml b/src/dune_pkg/opam_solver.ml
index 37da7dc1967..747e72a5588 100644
--- a/src/dune_pkg/opam_solver.ml
+++ b/src/dune_pkg/opam_solver.ml
@@ -559,8 +559,8 @@ module Solver = struct
       Input.virtual_role [ impl ]
   ;;
 
-  module Solver = Zeroinstall_solver.Make (Input)
-  module Diagnostics = Zeroinstall_solver.Diagnostics (Solver.Output)
+  module Solver = Solver_core.Make (Input)
+  module Diagnostics = Diagnostics.Make (Solver.Output)
 
   let solve context pkgs =
     let req = requirements ~context pkgs in
diff --git a/src/dune_pkg/solver_core.ml b/src/dune_pkg/solver_core.ml
index 270c1206cf6..bae411e0f38 100644
--- a/src/dune_pkg/solver_core.ml
+++ b/src/dune_pkg/solver_core.ml
@@ -10,6 +10,8 @@ open Fiber.O
 module Make (Model : S.SOLVER_INPUT) = struct
   (** We attach this data to each SAT variable. *)
   module SolverData = struct
+    [@@@ocaml.warning "-37"]
+
     type t =
       (* If the SAT variable is True then we selected this... *)
       | ImplElem of Model.impl
@@ -38,7 +40,7 @@ module Make (Model : S.SOLVER_INPUT) = struct
       ; dummy_impl : Model.impl option
       }
 
-    let is_dummy t impl =
+    let[@ocaml.warning "-32"] is_dummy t impl =
       match t.dummy_impl with
       | None -> false
       | Some dummy_impl -> dummy_impl == impl
diff --git a/src/dune_pkg/solver_core.mli b/src/dune_pkg/solver_core.mli
new file mode 100644
index 00000000000..abd2327f65f
--- /dev/null
+++ b/src/dune_pkg/solver_core.mli
@@ -0,0 +1,15 @@
+(** Select a compatible set of components to run a program.
+    See [Zeroinstall.Solver] for the instantiation of this functor on the
+    actual 0install types. *)
+module Make (Input : S.SOLVER_INPUT) : sig
+  module Output : S.SOLVER_RESULT with module Input = Input
+
+  (** [do_solve model req] finds an implementation matching the given requirements, plus any other implementations needed
+      to satisfy its dependencies.
+      @param closest_match
+        adds a lowest-ranked (but valid) implementation ([Input.dummy_impl]) to
+        every interface, so we can always select something. Useful for diagnostics.
+        Note: always try without [closest_match] first, or it may miss a valid solution.
+      @return None if the solve fails (only happens if [closest_match] is false). *)
+  val do_solve : closest_match:bool -> Input.Role.t -> Output.t option Fiber.t
+end
diff --git a/src/dune_pkg/zeroinstall_solver.ml b/src/dune_pkg/zeroinstall_solver.ml
deleted file mode 100644
index b6e110a797f..00000000000
--- a/src/dune_pkg/zeroinstall_solver.ml
+++ /dev/null
@@ -1,3 +0,0 @@
-module Make = Solver_core.Make
-module Diagnostics = Diagnostics.Make
-module S = S