Fixes #2353 -- document that we need PyPy 2.6+
diff --git a/docs/installation.rst b/docs/installation.rst
index 277e021..1caeb1f 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -10,7 +10,7 @@
 Supported platforms
 -------------------
 
-Currently we test ``cryptography`` on Python 2.6, 2.7, 3.3, 3.4 and PyPy
+Currently we test ``cryptography`` on Python 2.6, 2.7, 3.3, 3.4 and PyPy 2.6+
 on these operating systems.
 
 * x86-64 CentOS 7.x, 6.4 and CentOS 5.x