diff --git a/testing/web-platform/tests/css/requirements.txt b/testing/web-platform/tests/css/requirements.txt
index 9267157acaa3..b1fcbe638660 100644
--- a/testing/web-platform/tests/css/requirements.txt
+++ b/testing/web-platform/tests/css/requirements.txt
@@ -1,5 +1,5 @@
 six==1.10.0
 Template-Python==0.1.post1
-html5lib==0.9999999
+html5lib==0.999999999
 lxml==3.7.3
 mercurial==4.1