diff --git a/pkgs/development/python-modules/black/default.nix b/pkgs/development/python-modules/black/default.nix
index f48310ceebc..b95ed080e66 100644
--- a/pkgs/development/python-modules/black/default.nix
+++ b/pkgs/development/python-modules/black/default.nix
@@ -1,17 +1,28 @@
-{ stdenv, buildPythonPackage, fetchPypi, pythonOlder, attrs, click }:
+{ stdenv, buildPythonPackage, fetchPypi, pythonOlder
+, attrs, click, toml, appdirs
+, glibcLocales, pytest }:
 
 buildPythonPackage rec {
   pname = "black";
-  version = "18.4a0";
+  version = "18.6b4";
 
   disabled = pythonOlder "3.6";
 
   src = fetchPypi {
     inherit pname version;
-    sha256 = "04dffr4wmzs4vf2xj0cxp03hv04x0kk06qyzx6jjrp1mq0z3n2rr";
+    sha256 = "0i4sfqgz6w15vd50kbhi7g7rifgqlf8yfr8y78rypd56q64qn592";
   };
 
-  propagatedBuildInputs = [ attrs click ];
+  checkInputs =  [ pytest glibcLocales ];
+
+  checkPhase = ''
+    # no idea, why those fail.
+    LC_ALL="en_US.UTF-8" HOME="$NIX_BUILD_TOP" \
+      pytest \
+        -k "not test_cache_multiple_files and not test_failed_formatting_does_not_get_cached"
+  '';
+
+  propagatedBuildInputs = [ attrs appdirs click toml ];
 
   meta = with stdenv.lib; {
     description = "The uncompromising Python code formatter";