diff --git a/tests/requirements.txt b/tests/requirements.txt
index 327f563a..bbcdc7cc 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -13,3 +13,5 @@ unittest2==1.1.0
 # Fix InsecurePlatformWarning while creating py26 tox environment
 # https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings
 urllib3[secure]; python_version < '2.7.9'
+# Last idna compatible with Python 2.6 was idna 2.7.
+idna==2.7; python_version < '2.7'