diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index 4dbb61cc456..069a10cdba5 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -21540,11 +21540,15 @@ in {
 
     checkPhase = ''
       runHook preCheck
-      export LANG="en_US.UTF-8";
-      py.test;
+      export LANG="en_US.UTF-8"
+      py.test
       runHook postCheck
     '';
 
+    # Seems to fail unpredictably on Darwin. See http://hydra.nixos.org/build/49877419/nixlog/1
+    # for one example, but I've also seen ContextTests.test_set_verify_callback_exception fail.
+    doCheck = !stdenv.isDarwin;
+
     buildInputs = [ pkgs.openssl self.pytest pkgs.glibcLocales ];
     propagatedBuildInputs = [ self.cryptography self.pyasn1 self.idna ];
   };