diff --git a/pkgs/development/python-modules/portend/black-19.10b0.patch b/pkgs/development/python-modules/portend/black-19.10b0.patch
new file mode 100644
index 000000000000..e781139e3192
--- /dev/null
+++ b/pkgs/development/python-modules/portend/black-19.10b0.patch
@@ -0,0 +1,13 @@
+diff --git a/test_portend.py b/test_portend.py
+index b2de8c2..3f90276 100644
+--- a/test_portend.py
++++ b/test_portend.py
+@@ -21,7 +21,7 @@ def socket_infos():
+ 
+ 
+ def id_for_info(info):
+-    af, = info[:1]
++    (af,) = info[:1]
+     return str(af)
+ 
+ 
\ No newline at end of file
diff --git a/pkgs/development/python-modules/portend/default.nix b/pkgs/development/python-modules/portend/default.nix
index b7d730d6ae00..9cc88983a303 100644
--- a/pkgs/development/python-modules/portend/default.nix
+++ b/pkgs/development/python-modules/portend/default.nix
@@ -10,6 +10,7 @@ buildPythonPackage rec {
     sha256 = "19dc27bfb3c72471bd30a235a4d5fbefef8a7e31cab367744b5d87a205e7bfd9";
   };
 
+  patches = [ ./black-19.10b0.patch ];
   postPatch = ''
     substituteInPlace pytest.ini --replace "--flake8" ""
   '';