diff --git a/pkgs/development/python-modules/deform/default.nix b/pkgs/development/python-modules/deform/default.nix
index bc84df26a27..5698dcbe491 100644
--- a/pkgs/development/python-modules/deform/default.nix
+++ b/pkgs/development/python-modules/deform/default.nix
@@ -11,11 +11,6 @@ buildPythonPackage rec {
     sha256 = "1e912937650c1dbb830079dd9c039950762a230223a567740fbf1b23f1090367";
   };
 
-  postPatch = ''
-    substituteInPlace setup.py \
-      --replace "iso8601<=0.1.11" iso8601
-  '';
-
   propagatedBuildInputs = [
     chameleon
     colander