diff --git a/pkgs/by-name/un/unison/fix-ocamlfind-env.patch b/pkgs/by-name/un/unison/fix-ocamlfind-env.patch
new file mode 100644
index 000000000000..7e1a594cc339
--- /dev/null
+++ b/pkgs/by-name/un/unison/fix-ocamlfind-env.patch
@@ -0,0 +1,14 @@
+diff --git a/src/make_tools.ml b/src/make_tools.ml
+index a5792b6..4f4d037 100644
+--- a/src/make_tools.ml
++++ b/src/make_tools.ml
+@@ -475,7 +475,7 @@ let shell_internal ?(err_null = false) ?exit_status ?(input_str = "") cmd =
+     Unix.handle_unix_error (fun () ->
+       if err_null || input_str <> "" then
+         let (sh_out, sh_in, _) as sh_full =
+-          Unix.open_process_full cmd [|"PATH=" ^ env.$("PATH")|] in
++          Unix.open_process_full cmd (Array.append (Unix.environment ()) [|"PATH=" ^ env.$("PATH")|]) in
+         if input_str <> "" then begin
+           output_string sh_in input_str;
+           flush sh_in
+
diff --git a/pkgs/by-name/un/unison/package.nix b/pkgs/by-name/un/unison/package.nix
index 0907a7faca36..67cdcf72c012 100644
--- a/pkgs/by-name/un/unison/package.nix
+++ b/pkgs/by-name/un/unison/package.nix
@@ -21,6 +21,9 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-ynsu9jLGFtjlzmHZtOdLEH5G6eXFAhZs9UayYrmKqp0=";
   };
 
+  # Allow the build scripts to correctly call ocamlfind & detect dependencies
+  patches = [ ./fix-ocamlfind-env.patch ];
+
   strictDeps = true;
 
   nativeBuildInputs = [