diff --git a/0001-mlstdutils-std_utils.ml-Fix-for-OCaml-4.12.patch b/0001-mlstdutils-std_utils.ml-Fix-for-OCaml-4.12.patch
new file mode 100644
index 0000000..4a21db6
--- /dev/null
+++ b/0001-mlstdutils-std_utils.ml-Fix-for-OCaml-4.12.patch
@@ -0,0 +1,35 @@
+From cc4ecbe236914f9b391ecf3815008547472632f8 Mon Sep 17 00:00:00 2001
+From: "Richard W.M. Jones" <rjones@redhat.com>
+Date: Tue, 2 Mar 2021 10:39:15 +0000
+Subject: [PATCH] mlstdutils/std_utils.ml: Fix for OCaml 4.12.
+
+We were using a default function from somewhere called "compare"
+instead of the actual function (Pervasives.compare / Stdlib.compare).
+Since the wrong default function was used it had a different type from
+what we expected:
+
+File "std_utils.ml", line 312, characters 36-37:
+312 |       | (y, y') :: _ when cmp x y = 0 -> y'
+                                          ^
+Error: This expression has type int but an expression was expected of type
+         'weak1 list -> int
+---
+ common/mlstdutils/std_utils.ml | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/common/mlstdutils/std_utils.ml b/common/mlstdutils/std_utils.ml
+index 4237ea519..88477179a 100644
+--- a/common/mlstdutils/std_utils.ml
++++ b/common/mlstdutils/std_utils.ml
+@@ -307,7 +307,7 @@ module List = struct
+       | x::xs, y::ys, z::zs -> (x, y, z) :: combine3 xs ys zs
+       | _ -> invalid_arg "combine3"
+ 
+-    let rec assoc_lbl ?(cmp = compare) ~default x = function
++    let rec assoc_lbl ?(cmp = Pervasives.compare) ~default x = function
+       | [] -> default
+       | (y, y') :: _ when cmp x y = 0 -> y'
+       | _ :: ys -> assoc_lbl ~cmp ~default x ys
+-- 
+2.29.0.rc2
+
diff --git a/virt-v2v.spec b/virt-v2v.spec
index 671a21f..4b826d9 100644
--- a/virt-v2v.spec
+++ b/virt-v2v.spec
@@ -10,7 +10,7 @@
 Name:          virt-v2v
 Epoch:         1
 Version:       1.43.3
-Release:       2%{?dist}
+Release:       3%{?dist}
 Summary:       Convert a virtual machine to run on KVM
 
 License:       GPLv2+
@@ -26,6 +26,9 @@ Source2:       libguestfs.keyring
 # Maintainer script which helps with handling patches.
 Source3:       copy-patches.sh
 
+# Fix for OCaml 4.12.
+Patch1:        0001-mlstdutils-std_utils.ml-Fix-for-OCaml-4.12.patch
+
 %if !0%{?rhel}
 # libguestfs hasn't been built on i686 for a while since there is no
 # kernel built for this architecture any longer and libguestfs rather
@@ -263,6 +266,9 @@ rm $RPM_BUILD_ROOT%{_datadir}/bash-completion/completions/virt-v2v-copy-to-local
 
 
 %changelog
+* Tue Mar  2 2021 Richard W.M. Jones <rjones@redhat.com> - 1:1.43.3-3
+- Add fix for OCaml 4.12.
+
 * Wed Jan 27 2021 Fedora Release Engineering <releng@fedoraproject.org> - 1:1.43.3-2
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_34_Mass_Rebuild