diff --git a/doc/install.rst b/doc/install.rst
index 0324845..58910e2 100644
--- a/doc/install.rst
+++ b/doc/install.rst
@@ -42,6 +42,10 @@ Once you have installed all the necessary prerequisites a simple::
 
 will install the basic code.
 
+Note for rhel/centos 6: cffi depends on libffi-devel, and cryptography on openssl-devel to compile
+So you might want first to do:
+yum install libffi-devel openssl-devel
+
 After this you ought to be able to run the tests without an hitch.
 The tests are based on the pypy test environment, so::