diff --git a/bin/arg.ml b/bin/arg.ml
index 800eadfaf097..3cb497bc5dc9 100644
--- a/bin/arg.ml
+++ b/bin/arg.ml
@@ -122,3 +122,5 @@ let bytes =
   conv (decode, pp_print_int64)
 
 let context_name : Context_name.t conv = conv Context_name.conv
+
+let lib_name = conv Dune.Lib_name.conv
diff --git a/bin/arg.mli b/bin/arg.mli
index cfdafc28a947..cee2396a661f 100644
--- a/bin/arg.mli
+++ b/bin/arg.mli
@@ -36,3 +36,5 @@ val path : Path.t conv
 val package_name : Package.Name.t conv
 
 val profile : Profile.t conv
+
+val lib_name : Lib_name.t conv
diff --git a/bin/common.ml b/bin/common.ml
index 820dd5df49b9..7df82b5ad65f 100644
--- a/bin/common.ml
+++ b/bin/common.ml
@@ -48,7 +48,7 @@ type t =
   ; stats_trace_file : string option
   ; always_show_command_line : bool
   ; promote_install_files : bool
-  ; instrument_with : string list option
+  ; instrument_with : Dune.Lib_name.t list option
   }
 
 let workspace_file t = t.workspace_file
@@ -638,7 +638,7 @@ let term =
     in
     Arg.(
       value
-      & opt (some (list string)) None
+      & opt (some (list lib_name)) None
       & info [ "instrument-with" ] ~docs
           ~env:(Arg.env_var ~doc "DUNE_INSTRUMENT_WITH")
           ~docv:"BACKENDS" ~doc)
diff --git a/bin/common.mli b/bin/common.mli
index 2a9d7e7b97bc..b5e695c26992 100644
--- a/bin/common.mli
+++ b/bin/common.mli
@@ -28,7 +28,7 @@ val default_target : t -> Arg.Dep.t
 
 val prefix_target : t -> string -> string
 
-val instrument_with : t -> string list option
+val instrument_with : t -> Dune.Lib_name.t list option
 
 (** [set_common ?log common ~targets ~external_lib_deps_mode] is
     [set_dirs common] followed by [set_common_other common ~targets]. In
diff --git a/src/dune/main.mli b/src/dune/main.mli
index 7e41697b83b2..2505603ec994 100644
--- a/src/dune/main.mli
+++ b/src/dune/main.mli
@@ -22,7 +22,7 @@ val scan_workspace :
   -> ?x:Context_name.t
   -> ?capture_outputs:bool
   -> ?profile:Profile.t
-  -> ?instrument_with:string list
+  -> ?instrument_with:Lib_name.t list
   -> ancestor_vcs:Vcs.t option
   -> unit
   -> workspace Fiber.t
diff --git a/src/dune/workspace.ml b/src/dune/workspace.ml
index b4d4d7329884..99f91a20947e 100644
--- a/src/dune/workspace.ml
+++ b/src/dune/workspace.ml
@@ -470,7 +470,7 @@ module DB = struct
     type t =
       { x : Context_name.t option
       ; profile : Profile.t option
-      ; instrument_with : string list option
+      ; instrument_with : Lib_name.t list option
       ; path : Path.t option
       }
 
@@ -479,7 +479,7 @@ module DB = struct
       record
         [ ("x", option Context_name.to_dyn x)
         ; ("profile", option Profile.to_dyn profile)
-        ; ("instrument_with", option (list string) instrument_with)
+        ; ("instrument_with", option (list Lib_name.to_dyn) instrument_with)
         ; ("path", option Path.to_dyn path)
         ]
 
@@ -497,9 +497,6 @@ let workspace =
     let { DB.Settings.path; profile; instrument_with; x } =
       Memo.Run.Fdecl.get DB.Settings.t
     in
-    let instrument_with =
-      Option.map ~f:(List.map ~f:Lib_name.of_string) instrument_with
-    in
     match path with
     | None -> default ?x ?profile ?instrument_with ()
     | Some p -> load ?x ?profile ?instrument_with p
diff --git a/src/dune/workspace.mli b/src/dune/workspace.mli
index ff988c49e31c..1970aa4e0c11 100644
--- a/src/dune/workspace.mli
+++ b/src/dune/workspace.mli
@@ -78,7 +78,7 @@ val hash : t -> int
 val init :
      ?x:Context_name.t
   -> ?profile:Profile.t
-  -> ?instrument_with:string list
+  -> ?instrument_with:Lib_name.t list
   -> ?path:Path.t
   -> unit
   -> unit