diff --git a/src/saml2/client_base.py b/src/saml2/client_base.py
index 2f57d14..d36b9cf 100644
--- a/src/saml2/client_base.py
+++ b/src/saml2/client_base.py
@@ -301,6 +301,9 @@ class Base(Entity):
         except KeyError:
             pass
 
+        if sign is None:
+            sign = self.authn_requests_signed
+
         if (sign and self.sec.cert_handler.generate_cert()) or \
                 client_crt is not None:
             with self.lock: