diff --git a/0001-Fix-build-on-OCaml-4.13.1.patch b/0001-Fix-build-on-OCaml-4.13.1.patch
new file mode 100644
index 0000000..02e6995
--- /dev/null
+++ b/0001-Fix-build-on-OCaml-4.13.1.patch
@@ -0,0 +1,26 @@
+From a7f8c3308abf845beedd5a345c0627eab748f470 Mon Sep 17 00:00:00 2001
+From: "Richard W.M. Jones" <rjones@redhat.com>
+Date: Tue, 5 Oct 2021 11:00:13 +0100
+Subject: [PATCH] Fix build on OCaml 4.13.1
+
+https://github.com/aantron/markup.ml/issues/66
+---
+ test/dune | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/test/dune b/test/dune
+index e7a5928..8e52b33 100644
+--- a/test/dune
++++ b/test/dune
+@@ -1,7 +1,7 @@
+ (executable
+  (name test)
+  (libraries markup ounit2 test_support)
+- (flags (:standard -w +A-44-48)))
++ (flags (:standard -w +A-5-44-48)))
+ 
+ (rule
+  (alias runtest)
+-- 
+2.32.0
+
diff --git a/ocaml-markup.spec b/ocaml-markup.spec
index 64ab63f..af146a4 100644
--- a/ocaml-markup.spec
+++ b/ocaml-markup.spec
@@ -13,6 +13,9 @@ License:        MIT
 URL:            http://aantron.github.io/markup.ml/
 Source0:        https://github.com/aantron/markup.ml/archive/%{version}/%{srcname}-%{version}.tar.gz
 
+# https://github.com/aantron/markup.ml/issues/66
+Patch1:         0001-Fix-build-on-OCaml-4.13.1.patch
+
 BuildRequires:  ocaml >= 4.02.0
 BuildRequires:  ocaml-bisect-ppx-devel >= 2.0.0
 BuildRequires:  ocaml-dune >= 2.7.0