diff --git a/libname/ppx_inline_test_libname.ml b/libname/ppx_inline_test_libname.ml
index c7b4baf..d7f6104 100644
--- a/libname/ppx_inline_test_libname.ml
+++ b/libname/ppx_inline_test_libname.ml
@@ -20,4 +20,11 @@ let () =
       | Some lib -> libname := Some lib)
 ;;
 
-let get () = !libname;;
+let get () =
+  match !libname with
+  | None -> None
+  | Some lib ->
+    (match String.index lib ':' with
+     | exception Not_found -> Some (lib, None)
+     | i -> Some (String.sub lib 0 i, (Some (String.sub lib (i + 1) (String.length lib - i - 1)))))
+;;
diff --git a/libname/ppx_inline_test_libname.mli b/libname/ppx_inline_test_libname.mli
index ae24eb9..aa5de6e 100644
--- a/libname/ppx_inline_test_libname.mli
+++ b/libname/ppx_inline_test_libname.mli
@@ -1,3 +1,3 @@
 (** This library defines the command line argument -libname, shared by both ppx_bench
     and ppx_inline_test. *)
-val get : unit -> string option
+val get : unit -> (string * string option) option
diff --git a/src/ppx_inline_test.ml b/src/ppx_inline_test.ml
index b6e6b6e..9613f0e 100644
--- a/src/ppx_inline_test.ml
+++ b/src/ppx_inline_test.ml
@@ -309,10 +309,17 @@ let tags = E.tags
 
 let () =
   Driver.V2.register_transformation "inline-test" ~extensions:E.all ~enclose_impl:(fun ctxt loc ->
-      let partition = Stdlib.Filename.basename (Expansion_context.Base.input_name ctxt) in
-    match loc, Ppx_inline_test_libname.get () with
+      let libname_and_partition =
+        match Ppx_inline_test_libname.get () with
+        | None -> None
+        | Some (libname, Some partition) -> Some (libname, partition)
+        | Some (libname, None) ->
+          let partition = Stdlib.Filename.basename (Expansion_context.Base.input_name ctxt) in
+          Some (libname, partition)
+      in
+    match loc, libname_and_partition with
     | None, _ | _, None -> [], []
-    | Some loc, Some libname ->
+    | Some loc, Some (libname, partition) ->
       let loc = { loc with loc_ghost = true } in
       (* See comment in benchmark_accumulator.ml *)
       let header =