diff --git a/lwt-ocaml-405.patch b/lwt-ocaml-405.patch
new file mode 100644
index 0000000..22172fb
--- /dev/null
+++ b/lwt-ocaml-405.patch
@@ -0,0 +1,26 @@
+diff -ur lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd.old/src/unix/lwt_unix.ml lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd/src/unix/lwt_unix.ml
+--- lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd.old/src/unix/lwt_unix.ml	2014-04-21 13:52:40.000000000 +0100
++++ lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd/src/unix/lwt_unix.ml	2018-04-17 17:55:18.937430592 +0100
+@@ -599,6 +599,9 @@
+ #if ocaml_version >= (4, 01)
+   | O_CLOEXEC
+ #endif
++#if ocaml_version >= (4, 05)
++  | O_KEEPEXEC
++#endif
+ 
+ #if windows
+ 
+diff -ur lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd.old/src/unix/lwt_unix.mli lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd/src/unix/lwt_unix.mli
+--- lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd.old/src/unix/lwt_unix.mli	2014-04-21 13:52:40.000000000 +0100
++++ lwt-75b1dc1aefae75dc4ac6455f5a2688b3a52adabd/src/unix/lwt_unix.mli	2018-04-17 17:54:44.463413635 +0100
+@@ -318,6 +318,9 @@
+ #if ocaml_version >= (4, 01)
+   | O_CLOEXEC
+ #endif
++#if ocaml_version >= (4, 05)
++  | O_KEEPEXEC
++#endif
+ 
+ val openfile : string -> open_flag list -> file_perm -> file_descr Lwt.t
+   (** Wrapper for [Unix.openfile]. *)
diff --git a/ocaml-lwt.spec b/ocaml-lwt.spec
index 8baf35c..65febc4 100644
--- a/ocaml-lwt.spec
+++ b/ocaml-lwt.spec
@@ -11,6 +11,8 @@ License:        LGPLv2+ with exceptions
 URL:            http://ocsigen.org/lwt
 Source0:        https://github.com/ocsigen/lwt/archive/%{commit}/lwt-%{commit}.tar.gz
 
+# Patch to make this old LWT work with OCaml 4.05.
+Patch1:         lwt-ocaml-405.patch
 
 BuildRequires:  ocaml >= 3.10.0
 BuildRequires:  ocaml-ocamlbuild
@@ -44,6 +46,7 @@ developing applications that use %{name}.
 
 %prep
 %setup -q -n lwt-%{commit}
+%patch1 -p1
 
 mv README README.old
 iconv -f iso-8859-1 -t utf-8 < README.old > README