diff --git a/pkgs/development/tools/ocaml/merlin/4.x.nix b/pkgs/development/tools/ocaml/merlin/4.x.nix
index e55fd630cec9..f4c97b9642ec 100644
--- a/pkgs/development/tools/ocaml/merlin/4.x.nix
+++ b/pkgs/development/tools/ocaml/merlin/4.x.nix
@@ -1,6 +1,7 @@
 { lib
 , substituteAll
 , fetchurl
+, fetchpatch
 , ocaml
 , dune_3
 , buildDunePackage
@@ -56,12 +57,24 @@ buildDunePackage {
     sha256 = hashes."${version}";
   };
 
-  patches = [
+  patches = let
+    branch = lib.head (lib.tail (lib.splitString "-" version));
+    needsVimPatch = lib.versionOlder version "4.17" ||
+                    branch == "502" && lib.versionOlder version "5.2";
+  in
+  [
     (substituteAll {
       src = ./fix-paths.patch;
       dot_merlin_reader = "${dot-merlin-reader}/bin/dot-merlin-reader";
       dune = "${dune_3}/bin/dune";
     })
+  ] ++ lib.optionals needsVimPatch [
+    # https://github.com/ocaml/merlin/pull/1798
+    (fetchpatch {
+      name = "vim-python-12-syntax-warning-fix.patch";
+      url = "https://github.com/ocaml/merlin/commit/9e0c47b0d5fd0c4edc37c4c7ce927b155877557d.patch";
+      hash = "sha256-HmdTISE/s45C5cwLgsCHNUW6OAPSsvQ/GcJE6VDEobs=";
+    })
   ];
 
   strictDeps = true;
diff --git a/pkgs/development/tools/ocaml/merlin/default.nix b/pkgs/development/tools/ocaml/merlin/default.nix
index a80252c3dfbc..c37cac53430b 100644
--- a/pkgs/development/tools/ocaml/merlin/default.nix
+++ b/pkgs/development/tools/ocaml/merlin/default.nix
@@ -1,4 +1,4 @@
-{ lib, fetchurl, buildDunePackage, substituteAll
+{ lib, fetchurl, fetchpatch, buildDunePackage, substituteAll
 , dot-merlin-reader, dune_2, yojson, csexp, result, menhirSdk }:
 
 buildDunePackage rec {
@@ -18,6 +18,12 @@ buildDunePackage rec {
       dot_merlin_reader = "${dot-merlin-reader}/bin/dot-merlin-reader";
       dune = "${dune_2}/bin/dune";
     })
+    # https://github.com/ocaml/merlin/pull/1798
+    (fetchpatch {
+      name = "vim-python-12-syntax-warning-fix.patch";
+      url = "https://github.com/ocaml/merlin/commit/9e0c47b0d5fd0c4edc37c4c7ce927b155877557d.patch";
+      hash = "sha256-HmdTISE/s45C5cwLgsCHNUW6OAPSsvQ/GcJE6VDEobs=";
+    })
   ];
 
   strictDeps = true;