diff --git a/pkgs/development/python-modules/zcs/default.nix b/pkgs/development/python-modules/zcs/default.nix
index 9f22cd1dfc86..8ad26668bc5e 100644
--- a/pkgs/development/python-modules/zcs/default.nix
+++ b/pkgs/development/python-modules/zcs/default.nix
@@ -15,6 +15,10 @@ buildPythonPackage rec {
     sha256 = "sha256-ZoQgAaJy3kKHLljyKA0Oo/D1kefE8X9FlsGDSNt1nPw=";
   };
 
+  patches = [
+    ./fix-test-yaml.patch
+  ];
+
   propagatedBuildInputs = [ yacs ];
 
   pythonImportsCheck = [ "zcs" ];
diff --git a/pkgs/development/python-modules/zcs/fix-test-yaml.patch b/pkgs/development/python-modules/zcs/fix-test-yaml.patch
new file mode 100644
index 000000000000..a046f1808296
--- /dev/null
+++ b/pkgs/development/python-modules/zcs/fix-test-yaml.patch
@@ -0,0 +1,13 @@
+diff --git a/test/test_zcs.py b/test/test_zcs.py
+index e4981d3..893999f 100644
+--- a/test/test_zcs.py
++++ b/test/test_zcs.py
+@@ -65,7 +65,7 @@ class TestCfgNode(unittest.TestCase):
+         cfg = self.cfg.clone()
+         yamlp = pathjoin(tmpboxx(), "test.yaml")
+         cfg.dump(yamlp)
+-        cfg_dict = yaml.load(open(yamlp))
++        cfg_dict = yaml.load(open(yamlp), yaml.Loader)
+         cfgd = CfgNode(cfg_dict)
+         self.assertTrue(str(cfg.dump()) == str(cfgd.dump()))
+