diff --git a/jira/client.py b/jira/client.py
index 1325026b0..0cc9a0e13 100644
--- a/jira/client.py
+++ b/jira/client.py
@@ -2306,8 +2306,9 @@ def _create_kerberos_session(self, timeout, kerberos_options=None):
         from requests_kerberos import HTTPKerberosAuth
         from requests_kerberos import OPTIONAL
 
-        mutual_authentication = OPTIONAL
-        if kerberos_options.get('mutual_authentication') == 'DISABLED':
+        if kerberos_options.get('mutual_authentication', 'OPTIONAL') == 'OPTIONAL':
+            mutual_authentication = OPTIONAL
+        elif kerberos_options.get('mutual_authentication') == 'DISABLED':
             mutual_authentication = DISABLED
         else:
             raise ValueError("Unknown value for mutual_authentication: %s" %