diff --git a/prism/agents/ec2.py b/prism/agents/ec2.py
index e441762..22a2ad6 100644
--- a/prism/agents/ec2.py
+++ b/prism/agents/ec2.py
@@ -380,7 +380,7 @@ def add_ingress_rule(self,
                     'IpProtocol': 'tcp',
                     'FromPort': 22,
                     'ToPort': 22,
-                    'Ipv6Ranges': [{'CidrIpv6': f'{external_ip}'}]
+                    'Ipv6Ranges': [{'CidrIpv6': f'{external_ip}/128'}]
                 },
             ]