diff --git a/moto/rds/utils.py b/moto/rds/utils.py
index b890ff9b5039..5f83482ce7d3 100644
--- a/moto/rds/utils.py
+++ b/moto/rds/utils.py
@@ -34,8 +34,10 @@ class DbInstanceEngine(str, Enum):
     CUSTOM_SQLSERVER_EE = "custom-sqlserver-ee"
     CUSTOM_SQLSERVER_SE = "custom-sqlserver-se"
     CUSTOM_SQLSERVER_WEB = "custom-sqlserver-web"
+    DOCDB = "docdb"
     MARIADB = "mariadb"
     MYSQL = "mysql"
+    NEPTUNE = "neptune"
     ORACLE_EE = "oracle-ee"
     ORACLE_EE_CDB = "oracle-ee-cdb"
     ORACLE_SE2 = "oracle-se2"