--- /usr/portage/sci-libs/vtk/vtk-7.1.0.ebuild	2017-03-03 08:35:54.334402533 +0100
+++ vtk-7.1.0-r1.ebuild	2017-03-15 12:07:59.566482984 +0100
@@ -17,10 +17,10 @@
 	"
 
 LICENSE="BSD LGPL-2"
@@ -95,6 +95,7 @@
 	virtual/opengl
 	web? (
 		${WEBAPP_DEPEND}
+		dev-python/six[${PYTHON_USEDEP}]
 		dev-python/autobahn[${PYTHON_USEDEP}]
 		dev-python/twisted-core[${PYTHON_USEDEP}]
 		dev-python/zope-interface[${PYTHON_USEDEP}]
@@ -246,6 +247,7 @@
 			-DVTK_PYTHON_INCLUDE_DIR="$(python_get_includedir)"
 			-DVTK_PYTHON_LIBRARY="$(python_get_library_path)"
 			-DVTK_PYTHON_SETUP_ARGS:STRING="--prefix=${EPREFIX} --root=${D}"
+			-DVTK_USE_SYSTEM_SIX=ON
 		)
 	fi