diff --git a/pkgs/development/compilers/mlton/20210117-binary.nix b/pkgs/development/compilers/mlton/20210117-binary.nix
index 523d46ed8c39..f95c6e330b6f 100644
--- a/pkgs/development/compilers/mlton/20210117-binary.nix
+++ b/pkgs/development/compilers/mlton/20210117-binary.nix
@@ -36,7 +36,7 @@ stdenv.mkDerivation rec {
     (fetchpatch {
       name = "remove-duplicate-if.patch";
       url = "https://github.com/MLton/mlton/commit/22002cd0a53a1ab84491d74cb8dc6a4e50c1f7b7.patch";
-      decode = "sed -e 's|Makefile\.binary|Makefile|g'";
+      decode = "sed -e 's|Makefile\\.binary|Makefile|g'";
       hash = "sha256-Gtmc+OIh+m7ordSn74fpOKVDQDtYyLHe6Le2snNCBYQ=";
     })
   ];