diff --git a/pkgs/development/python-modules/xarray/default.nix b/pkgs/development/python-modules/xarray/default.nix
index b419e7f5cc7e..d547d4a15d1b 100644
--- a/pkgs/development/python-modules/xarray/default.nix
+++ b/pkgs/development/python-modules/xarray/default.nix
@@ -5,6 +5,7 @@
 , numpy
 , pandas
 , python
+, isPy3k
 }:
 
 buildPythonPackage rec {
@@ -20,7 +21,7 @@ buildPythonPackage rec {
   propagatedBuildInputs = [numpy pandas];
 
   checkPhase = ''
-    py.test $out/${python.sitePackages}
+    pytest $out/${python.sitePackages}
   '';
 
   # There always seem to be broken tests...