Index: Makefile
===================================================================
--- Makefile	(revision 551704)
+++ Makefile	(working copy)
@@ -33,7 +33,7 @@
 
 # Actually 3.5.3+
 USES=		python:3.5+
-USE_PYTHON=	autoplist distutils
+USE_PYTHON=	autoplist distutils cython
 
 .include <bsd.port.pre.mk>
 
@@ -42,6 +42,9 @@
 		${PYTHON_PKGNAMEPREFIX}typing-extensions>=3.6.5:devel/py-typing-extensions@${PY_FLAVOR}
 .endif
 
+pre-configure:
+	@${TOUCH} ${WRKSRC}/aiohttp/*.pyx
+
 post-install:
 	${STRIP_CMD} ${STAGEDIR}${PYTHONPREFIX_SITELIBDIR}/aiohttp/*.so