diff --git a/0001-ocaml-Fix-bug-in-asynch-copy-test.patch b/0001-ocaml-Fix-bug-in-asynch-copy-test.patch
new file mode 100644
index 0000000..d59a39b
--- /dev/null
+++ b/0001-ocaml-Fix-bug-in-asynch-copy-test.patch
@@ -0,0 +1,52 @@
+From 0475bfe04a527051c0a37af59a733c4c8554e427 Mon Sep 17 00:00:00 2001
+From: "Richard W.M. Jones" <rjones@redhat.com>
+Date: Fri, 17 Apr 2020 22:23:56 +0100
+Subject: [PATCH] ocaml: Fix bug in asynch copy test.
+
+This program had a subtle bug: If we've read everything from the
+source, but there are still source commands in flight, AND it happens
+that there are no destination commands in flight, then the loop
+finishes prematurely.  This is particularly evident when you run the
+test on a slow machine (armv7 in Koji is illustrative).  The fix is to
+check that there are no commands in flight either from the source or
+to the destination.
+
+(I actually discovered this when writing the golang bindings which
+copied from the OCaml version, but forgot to make the correction to
+the original.)
+---
+ ocaml/examples/asynch_copy.ml    | 3 ++-
+ ocaml/tests/test_590_aio_copy.ml | 3 ++-
+ 2 files changed, 4 insertions(+), 2 deletions(-)
+
+diff --git a/ocaml/examples/asynch_copy.ml b/ocaml/examples/asynch_copy.ml
+index d5dcc60..7132f57 100644
+--- a/ocaml/examples/asynch_copy.ml
++++ b/ocaml/examples/asynch_copy.ml
+@@ -41,7 +41,8 @@ let asynch_copy src dst =
+   (* The main loop which runs until we have finished reading and
+    * there are no more commands in flight.
+    *)
+-  while !soff < size || NBD.aio_in_flight dst > 0 do
++  while !soff < size || NBD.aio_in_flight src > 0 || NBD.aio_in_flight dst > 0
++  do
+     (* If we're able to submit more reads from the source then do so now. *)
+     if !soff < size && NBD.aio_in_flight src < max_reads_in_flight then (
+       let bs = min bs (size -^ !soff) in
+diff --git a/ocaml/tests/test_590_aio_copy.ml b/ocaml/tests/test_590_aio_copy.ml
+index ac490ef..e3cd59d 100644
+--- a/ocaml/tests/test_590_aio_copy.ml
++++ b/ocaml/tests/test_590_aio_copy.ml
+@@ -64,7 +64,8 @@ let asynch_copy src dst =
+   (* The main loop which runs until we have finished reading and
+    * there are no more commands in flight.
+    *)
+-  while !soff < size || NBD.aio_in_flight dst > 0 do
++  while !soff < size || NBD.aio_in_flight src > 0 || NBD.aio_in_flight dst > 0
++  do
+     (* If we're able to submit more reads from the source then do so now. *)
+     if !soff < size && NBD.aio_in_flight src < max_reads_in_flight then (
+       let bs = min bs (size -^ !soff) in
+-- 
+2.25.0
+
diff --git a/libnbd.spec b/libnbd.spec
index 7cde48c..ff4f05d 100644
--- a/libnbd.spec
+++ b/libnbd.spec
@@ -9,7 +9,7 @@
 
 Name:           libnbd
 Version:        1.3.6
-Release:        3%{?dist}
+Release:        4%{?dist}
 Summary:        NBD client library in userspace
 
 License:        LGPLv2+
@@ -22,6 +22,9 @@ Source1:        http://libguestfs.org/download/libnbd/%{source_directory}/%{name
 # https://pgp.key-server.io/pks/lookup?search=rjones%40redhat.com&fingerprint=on&op=vindex
 Source2:       libguestfs.keyring
 
+# Upstream patch to fix one of the tests that fails on slow machines.
+Patch1:        0001-ocaml-Fix-bug-in-asynch-copy-test.patch
+
 %if 0%{patches_touch_autotools}
 BuildRequires: autoconf, automake, libtool
 %endif
@@ -277,6 +280,7 @@ make %{?_smp_mflags} check || {
 %changelog
 * Fri Apr 17 2020 Richard W.M. Jones <rjones@redhat.com> - 1.3.6-3
 - OCaml 4.11.0 pre-release
+- Add upstream patch to fix one of the tests that fails on slow machines.
 
 * Thu Apr 02 2020 Richard W.M. Jones <rjones@redhat.com> - 1.3.6-2
 - Update all OCaml dependencies for RPM 4.16.