diff --git a/holochain_client/api/common/types.py b/holochain_client/api/common/types.py
index 84afd9e..ac798ce 100644
--- a/holochain_client/api/common/types.py
+++ b/holochain_client/api/common/types.py
@@ -1,6 +1,8 @@
+from typing import Tuple
+
 DnaHash = bytes
 AgentPubKey = bytes
-CellId = [DnaHash, AgentPubKey]
+CellId = Tuple[DnaHash, AgentPubKey]
 ZomeName = str
 FunctionName = str
 RoleName = str