diff --git a/pkgs/development/ocaml-modules/extlib/1.7.7.nix b/pkgs/development/ocaml-modules/extlib/1.7.7.nix
new file mode 100644
index 00000000000..3314ebcb9b5
--- /dev/null
+++ b/pkgs/development/ocaml-modules/extlib/1.7.7.nix
@@ -0,0 +1,11 @@
+# Older version of extlib for Haxe 4.0 and 4.1.
+# May be replaceable by the next extlib + extlib-base64 release.
+{ fetchurl, ocaml_extlib }:
+
+ocaml_extlib.overrideAttrs (_: rec {
+  version = "1.7.7";
+  src = fetchurl {
+    url = "https://github.com/ygrek/ocaml-extlib/releases/download/${version}/extlib-${version}.tar.gz";
+    sha256 = "1sxmzc1mx3kg62j8kbk0dxkx8mkf1rn70h542cjzrziflznap0s1";
+  };
+})
diff --git a/pkgs/top-level/ocaml-packages.nix b/pkgs/top-level/ocaml-packages.nix
index b8c8b0a9d93..c5328f378b6 100644
--- a/pkgs/top-level/ocaml-packages.nix
+++ b/pkgs/top-level/ocaml-packages.nix
@@ -1018,7 +1018,11 @@ let
 
     ocaml-protoc = callPackage ../development/ocaml-modules/ocaml-protoc { };
 
-    ocaml_extlib = callPackage ../development/ocaml-modules/extlib { };
+    ocaml_extlib = ocaml_extlib-1-7-8;
+
+    ocaml_extlib-1-7-8 = callPackage ../development/ocaml-modules/extlib { };
+
+    ocaml_extlib-1-7-7 = callPackage ../development/ocaml-modules/extlib/1.7.7.nix { };
 
     ocb-stubblr = callPackage ../development/ocaml-modules/ocb-stubblr { };