diff --git a/src/irmin-pack/unix/gc.ml b/src/irmin-pack/unix/gc.ml
index 1da61e67f6..dd63407128 100644
--- a/src/irmin-pack/unix/gc.ml
+++ b/src/irmin-pack/unix/gc.ml
@@ -285,8 +285,9 @@ module Make (Args : Gc_args.S) = struct
 
   let finalise_without_swap t =
     let* status = Async.await t.task in
-    match status with
-    | `Success ->
+    let gc_output = read_gc_output ~root:t.root ~generation:t.generation in
+    match (status, gc_output) with
+    | `Success, Ok _ ->
         Lwt.return (t.latest_gc_target_offset, t.new_suffix_start_offset)
     | _ ->
         let gc_output = read_gc_output ~root:t.root ~generation:t.generation in
diff --git a/src/irmin-pack/unix/gc_worker.ml b/src/irmin-pack/unix/gc_worker.ml
index 1700322258..5ab402e504 100644
--- a/src/irmin-pack/unix/gc_worker.ml
+++ b/src/irmin-pack/unix/gc_worker.ml
@@ -371,6 +371,7 @@ module Make (Args : Gc_args.S) = struct
           run ~generation ~new_files_path root commit_key
             new_suffix_start_offset)
     in
+    Errs.log_if_error "gc run" result;
     let write_result = write_gc_output ~root ~generation result in
     write_result |> Errs.log_if_error "writing gc output"
   (* No need to raise or log if [result] is [Error _], we've written it in
diff --git a/src/irmin-pack/unix/io_errors.ml b/src/irmin-pack/unix/io_errors.ml
index fd1dd736d6..2a3edd53ac 100644
--- a/src/irmin-pack/unix/io_errors.ml
+++ b/src/irmin-pack/unix/io_errors.ml
@@ -28,7 +28,7 @@ module type S = sig
   val log_error : string -> [< t ] -> unit
   val catch : (unit -> 'a) -> ('a, t) result
   val raise_if_error : ('a, [< t ]) result -> 'a
-  val log_if_error : string -> (unit, [< t ]) result -> unit
+  val log_if_error : string -> ('a, [< t ]) result -> unit
 end
 
 module Make (Io : Io.S) : S with module Io = Io = struct