diff --git a/moto/ec2/models.py b/moto/ec2/models.py
index 6038db09..b7ab1266 100644
--- a/moto/ec2/models.py
+++ b/moto/ec2/models.py
@@ -1964,7 +1964,7 @@ class ElasticAddress(object):
 
     @property
     def physical_resource_id(self):
-        return self.allocation_id
+        return self.allocation_id if self.allocation_id else self.public_ip
 
     def get_cfn_attribute(self, attribute_name):
         from moto.cloudformation.exceptions import UnformattedGetAttTemplateException