diff --git a/README.md b/README.md
index 4027eb4..92aa9b5 100644
--- a/README.md
+++ b/README.md
@@ -1170,7 +1170,7 @@ This may be useful during the process of porting existing code to Eio.
 
 - [lib_eio/eio.mli](lib_eio/eio.mli) documents Eio's public API.
 - [doc/rationale.md](doc/rationale.md) describes some of Eio's design tradeoffs in more detail.
-- [doc/eio_null.md](doc/eio_null.md) is a skeleton Eio backend with no actual IO.
+- [lib_eio/mock/backend.ml](lib_eio/mock/backend.ml) is a skeleton Eio backend with no actual IO.
 
 Some background about the effects system can be found in:
 
diff --git a/doc/dune b/doc/dune
index dfe58d8..16d9c90 100644
--- a/doc/dune
+++ b/doc/dune
@@ -1,4 +1,4 @@
 (mdx
   (package eio_main)
   (packages eio_main)
-  (files multicore.md eio_null.md))
+  (files multicore.md))
diff --git a/doc/eio_null.md b/doc/eio_null.md
deleted file mode 100644
index 2000200..0000000
--- a/doc/eio_null.md
+++ /dev/null
@@ -1,104 +0,0 @@
-```ocaml
-# #require "eio.utils";;
-```
-
-# A dummy Eio backend with no actual effects
-
-This is very inefficient and not thread-safe, but it demonstrates the idea.
-A real backend would typically pass `main` some way to interact with it, like the other backends do.
-
-```ocaml
-open Eio.Std
-
-(* An Eio backend with no actual IO *)
-module Eio_null = struct
-  module Fiber_context = Eio.Private.Fiber_context
-  module Effect = Eio.Private.Effect    (* For compatibility with 4.12+domains *)
-
-  (* The scheduler could just return [unit], but this is clearer. *)
-  type exit = Exit_scheduler
-
-  type t = {
-    (* Suspended fibers waiting to run again.
-       A real system would probably use [Eio_utils.Lf_queue]. *)
-    mutable run_q : (unit -> exit) list;
-  }
-
-  (* Resume the next runnable fiber, if any. *)
-  let schedule t : exit =
-    match t.run_q with
-    | f :: fs -> t.run_q <- fs; f ()
-    | [] -> Exit_scheduler      (* Finished (or deadlocked) *)
-
-  (* Run [main] in an Eio main loop. *)
-  let run main =
-    let t = { run_q = [] } in
-    let rec fork ~new_fiber:fiber fn =
-      (* Create a new fiber and run [fn] in it. *)
-      Effect.Deep.match_with fn ()
-        { retc = (fun () -> Fiber_context.destroy fiber; schedule t);
-          exnc = (fun ex -> Fiber_context.destroy fiber; raise ex);
-          effc = fun (type a) (e : a Effect.t) : ((a, exit) Effect.Deep.continuation -> exit) option ->
-            match e with
-            | Eio.Private.Effects.Suspend f -> Some (fun k ->
-                (* Ask [f] to register whatever callbacks are needed to resume the fiber.
-                   e.g. it might register a callback with a promise, for when that's resolved. *)
-                f fiber (function
-                    (* The fiber is ready to run again. Add it to the queue. *)
-                    | Ok v -> t.run_q <- t.run_q @ [fun () -> Effect.Deep.continue k v]
-                    | Error ex -> t.run_q <- t.run_q @ [fun () -> Effect.Deep.discontinue k ex]
-                  );
-                (* Switch to the next runnable fiber while this one's blocked. *)
-                schedule t
-              )
-            | Eio.Private.Effects.Fork (new_fiber, f) -> Some (fun k ->
-                (* Arrange for the forking fiber to run immediately after the new one. *)
-                t.run_q <- Effect.Deep.continue k :: t.run_q;
-                (* Create and run the new fiber (using fiber context [new_fiber]). *)
-                fork ~new_fiber f
-              )
-            | Eio.Private.Effects.Get_context -> Some (fun k ->
-                Effect.Deep.continue k fiber
-              )
-            | Eio.Private.Effects.Trace -> Some (fun k ->
-                Effect.Deep.continue k Eio.Private.default_traceln
-              )
-            | _ -> None
-        }
-    in
-    let new_fiber = Fiber_context.make_root () in
-    let Exit_scheduler = fork ~new_fiber main in
-    ()
-end
-```
-
-It supports forking, tracing, suspending and cancellation:
-
-```ocaml
-# Eio_null.run @@ fun () ->
-  let s = Eio.Stream.create 1 in
-  try
-    Fiber.both
-      (fun () ->
-         for x = 1 to 3 do
-           traceln "Sending %d" x;
-           Eio.Stream.add s x
-         done;
-         raise Exit
-      )
-      (fun () ->
-         while true do
-           traceln "Got %d" (Eio.Stream.take s)
-         done
-      )
-  with Exit ->
-    traceln "Finished!";;
-+Sending 1
-+Sending 2
-+Got 1
-+Got 2
-+Sending 3
-+Got 3
-+Finished!
-- : unit = ()
-```
diff --git a/lib_eio/mock/backend.ml b/lib_eio/mock/backend.ml
new file mode 100644
index 0000000..9164ea5
--- /dev/null
+++ b/lib_eio/mock/backend.ml
@@ -0,0 +1,60 @@
+module Fiber_context = Eio.Private.Fiber_context
+module Effect = Eio.Private.Effect    (* For compatibility with 4.12+domains *)
+module Lf_queue = Eio_utils.Lf_queue
+
+(* The scheduler could just return [unit], but this is clearer. *)
+type exit = Exit_scheduler
+
+type t = {
+  (* Suspended fibers waiting to run again.
+     [Lf_queue] is like [Stdlib.Queue], but is thread-safe (lock-free) and
+     allows pushing items to the head too, which we need. *)
+  mutable run_q : (unit -> exit) Lf_queue.t;
+}
+
+(* Resume the next runnable fiber, if any. *)
+let schedule t : exit =
+  match Lf_queue.pop t.run_q with
+  | Some f -> f ()
+  | None -> Exit_scheduler      (* Finished (or deadlocked) *)
+
+(* Run [main] in an Eio main loop. *)
+let run main =
+  let t = { run_q = Lf_queue.create () } in
+  let rec fork ~new_fiber:fiber fn =
+    (* Create a new fiber and run [fn] in it. *)
+    Effect.Deep.match_with fn ()
+      { retc = (fun () -> Fiber_context.destroy fiber; schedule t);
+        exnc = (fun ex -> Fiber_context.destroy fiber; raise ex);
+        effc = fun (type a) (e : a Effect.t) : ((a, exit) Effect.Deep.continuation -> exit) option ->
+          match e with
+          | Eio.Private.Effects.Suspend f -> Some (fun k ->
+              (* Ask [f] to register whatever callbacks are needed to resume the fiber.
+                 e.g. it might register a callback with a promise, for when that's resolved. *)
+              f fiber (function
+                  (* The fiber is ready to run again. Add it to the queue. *)
+                  | Ok v -> Lf_queue.push t.run_q (fun () -> Effect.Deep.continue k v)
+                  | Error ex -> Lf_queue.push t.run_q (fun () -> Effect.Deep.discontinue k ex)
+                );
+              (* Switch to the next runnable fiber while this one's blocked. *)
+              schedule t
+            )
+          | Eio.Private.Effects.Fork (new_fiber, f) -> Some (fun k ->
+              (* Arrange for the forking fiber to run immediately after the new one. *)
+              Lf_queue.push_head t.run_q (Effect.Deep.continue k);
+              (* Create and run the new fiber (using fiber context [new_fiber]). *)
+              fork ~new_fiber f
+            )
+          | Eio.Private.Effects.Get_context -> Some (fun k ->
+              Effect.Deep.continue k fiber
+            )
+          | Eio.Private.Effects.Trace -> Some (fun k ->
+              Effect.Deep.continue k Eio.Private.default_traceln
+            )
+          | _ -> None
+      }
+  in
+  let new_fiber = Fiber_context.make_root () in
+  let result = ref None in
+  let Exit_scheduler = fork ~new_fiber (fun () -> result := Some (main ())) in
+  Option.get !result
diff --git a/lib_eio/mock/backend.mli b/lib_eio/mock/backend.mli
new file mode 100644
index 0000000..3aa9f8e
--- /dev/null
+++ b/lib_eio/mock/backend.mli
@@ -0,0 +1,4 @@
+(** A dummy Eio backend with no actual IO. *)
+
+val run : (unit -> 'a) -> 'a
+(** [run fn] runs an event loop and then calls [fn env] within it. *)
diff --git a/lib_eio/mock/dune b/lib_eio/mock/dune
index bce09eb..a8bc406 100644
--- a/lib_eio/mock/dune
+++ b/lib_eio/mock/dune
@@ -1,4 +1,4 @@
 (library
   (name eio_mock)
   (public_name eio.mock)
-  (libraries eio))
+  (libraries eio eio.utils))
diff --git a/lib_eio/mock/eio_mock.ml b/lib_eio/mock/eio_mock.ml
index 4d11c48..c04200f 100644
--- a/lib_eio/mock/eio_mock.ml
+++ b/lib_eio/mock/eio_mock.ml
@@ -2,3 +2,4 @@ module Action = Action
 module Handler = Handler
 module Flow = Flow
 module Net = Net
+module Backend = Backend
diff --git a/lib_eio/mock/eio_mock.mli b/lib_eio/mock/eio_mock.mli
index d59b890..1d59b2d 100644
--- a/lib_eio/mock/eio_mock.mli
+++ b/lib_eio/mock/eio_mock.mli
@@ -80,7 +80,7 @@ module Handler : sig
   (** [run_default_action t] runs the default handler passed to {!make}. *)
 end
 
-(** {2 Pre-defined mocks *)
+(** {2 Pre-defined mocks} *)
 
 (** Mock {!Eio.Flow} sources and sinks. *)
 module Flow : sig
@@ -148,3 +148,10 @@ module Net : sig
     unit
   (** [on_accept socket actions] configures how to respond when the server calls "accept". *)
 end
+
+(** {2 Backend for mocks}
+
+    The mocks can be used with any backend, but if you don't need any IO then you can use this one
+    to avoid a dependency on eio_main. *)
+
+module Backend = Backend
diff --git a/tests/buf_reader.md b/tests/buf_reader.md
index cf149ee..6982140 100644
--- a/tests/buf_reader.md
+++ b/tests/buf_reader.md
@@ -1,6 +1,5 @@
 ```ocaml
 # #require "eio";;
-# #require "eio.mock";;
 ```
 ```ocaml
 module R = Eio.Buf_read;;
@@ -599,6 +598,8 @@ Exception: Failure "Unexpected data after parsing (at offset 4)".
 ## Test using mock flow
 
 ```ocaml
+# #require "eio.mock";;
+
 # let flow = Eio_mock.Flow.make "flow" in
   Eio_mock.Flow.on_read flow [
     `Return "foo\nba";
diff --git a/tests/mocks.md b/tests/mocks.md
index d728736..635b0dd 100644
--- a/tests/mocks.md
+++ b/tests/mocks.md
@@ -1,7 +1,6 @@
 ## Setup
 
 ```ocaml
-# #require "eio_main";;
 # #require "eio.mock";;
 ```
 
@@ -14,7 +13,7 @@ let stdout = Eio_mock.Flow.make "stdout"
 ## Flows
 
 ```ocaml
-# Eio_main.run @@ fun _ ->
+# Eio_mock.Backend.run @@ fun _ ->
   Eio_mock.Flow.on_read stdin [
     `Return "chunk1";
     `Return "chunk2";
@@ -47,7 +46,7 @@ let echo_server ~net addr =
 The server handles a connection:
 
 ```ocaml
-# Eio_main.run @@ fun _ ->
+# Eio_mock.Backend.run @@ fun _ ->
   let net = Eio_mock.Net.make "mocknet" in
   let listening_socket = Eio_mock.Net.listening_socket "tcp/80" in
   Eio_mock.Net.on_listen net [`Return listening_socket];
@@ -66,3 +65,37 @@ The server handles a connection:
 +tcp/80: closed
 - : unit = ()
 ```
+
+## Backend
+
+`Eio_mock.Backend` supports forking, tracing, suspending and cancellation:
+
+```ocaml
+# Eio_mock.Backend.run @@ fun () ->
+  let s = Eio.Stream.create 1 in
+  try
+    Fiber.both
+      (fun () ->
+         for x = 1 to 3 do
+           traceln "Sending %d" x;
+           Eio.Stream.add s x
+         done;
+         raise Exit
+      )
+      (fun () ->
+         while true do
+           traceln "Got %d" (Eio.Stream.take s)
+         done
+      )
+  with Exit ->
+    traceln "Finished!";;
++Sending 1
++Sending 2
++Got 1
++Got 2
++Sending 3
++Got 3
++Finished!
+- : unit = ()
+```
+
diff --git a/tests/test_switch.md b/tests/test_switch.md
index 4cb9f9d..fbdd6cb 100644
--- a/tests/test_switch.md
+++ b/tests/test_switch.md
@@ -1,14 +1,14 @@
 # Setting up the environment
 
 ```ocaml
-# #require "eio_main";;
+# #require "eio.mock";;
 ```
 
 ```ocaml
 open Eio.Std
 
-let run (fn : Switch.t -> unit) =
-  Eio_main.run @@ fun _e ->
+let run (fn : Switch.t -> _) =
+  Eio_mock.Backend.run @@ fun () ->
   Switch.run fn
 ```
 
@@ -125,10 +125,7 @@ Exception: Failure "Cancel".
 You can't use a switch after leaving its scope:
 
 ```ocaml
-# let sw =
-    let x = ref None in
-    run (fun sw -> x := Some sw);
-    Option.get !x;;
+# let sw = run Fun.id;;
 val sw : Switch.t = <abstr>
 # Switch.check sw;;
 Exception: Invalid_argument "Switch finished!".