diff --git a/pkgs/development/python-modules/sphinx/default.nix b/pkgs/development/python-modules/sphinx/default.nix
index bae27c6133e..4639cf43d31 100644
--- a/pkgs/development/python-modules/sphinx/default.nix
+++ b/pkgs/development/python-modules/sphinx/default.nix
@@ -51,6 +51,12 @@ buildPythonPackage rec {
   postPatch = ''
     substituteInPlace setup.py \
       --replace "docutils>=0.14,<0.18" "docutils>=0.14"
+
+    # remove impurity caused by date inclusion 
+    # https://github.com/sphinx-doc/sphinx/blob/master/setup.cfg#L4-L6
+    substituteInPlace setup.cfg \
+      --replace "tag_build = .dev" "" \
+      --replace "tag_date = true" ""
   '';
 
   propagatedBuildInputs = [