From 1d8ca4a8520bebc572a43430ed4feeeec0cefff6 Mon Sep 17 00:00:00 2001
From: Lewis Gaul <lewis.gaul@gmail.com>
Date: Thu, 22 Jun 2023 04:29:05 -0700
Subject: [PATCH] Use same structure as delete_route() for determining cidr
 string

---
 moto/ec2/models/route_tables.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/moto/ec2/models/route_tables.py b/moto/ec2/models/route_tables.py
index 51c8e2e76708..9582f116746a 100644
--- a/moto/ec2/models/route_tables.py
+++ b/moto/ec2/models/route_tables.py
@@ -448,6 +448,11 @@ def replace_route(
         interface_id: Optional[str] = None,
         vpc_peering_connection_id: Optional[str] = None,
     ) -> Route:
+        cidr = destination_cidr_block
+        if destination_ipv6_cidr_block:
+            cidr = destination_ipv6_cidr_block
+        if destination_prefix_list_id:
+            cidr = destination_prefix_list_id
         route_table = self.get_route_table(route_table_id)
         route_id = generate_route_id(
             route_table.id, destination_cidr_block, destination_ipv6_cidr_block
@@ -455,11 +460,6 @@ def replace_route(
         try:
             route = route_table.routes[route_id]
         except KeyError:
-            cidr = (
-                destination_cidr_block
-                if destination_cidr_block
-                else destination_ipv6_cidr_block
-            )
             # This should be 'raise InvalidRouteError(route_table_id, cidr)' in
             # line with the delete_route() equivalent, but for some reason AWS
             # returns InvalidParameterValue instead in this case.