diff --git a/pkgs/development/python-modules/rfc3339-validator/default.nix b/pkgs/development/python-modules/rfc3339-validator/default.nix
index f51a232550b..07bc719698a 100644
--- a/pkgs/development/python-modules/rfc3339-validator/default.nix
+++ b/pkgs/development/python-modules/rfc3339-validator/default.nix
@@ -1,5 +1,6 @@
 { lib
 , buildPythonPackage
+, fetchpatch
 , fetchPypi
 , pytestCheckHook
 , hypothesis
@@ -17,6 +18,15 @@ buildPythonPackage rec {
     sha256 = "7a578aa0740e9ee2b48356fe1f347139190c4c72e27f303b3617054efd15df32";
   };
 
+  patches = [
+    # Fixes test failure on darwin. Filed upstream: https://github.com/naimetti/rfc3339-validator/pull/3.
+    # Not yet merged.
+    (fetchpatch {
+      url = "https://github.com/rmcgibbo/rfc3339-validator/commit/4b6bb62c30bd158d3b4663690dcba1084ac31770.patch";
+      sha256 = "0h9k82hhmp2xfzn49n3i47ws3rpm9lvfs2rjrds7hgx5blivpwl6";
+    })
+  ];
+
   propagatedBuildInputs = [ six ];
 
   checkInputs = [ pytestCheckHook hypothesis strict-rfc3339 ];