diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 4ef863a4805..a20affafee7 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -787,7 +787,7 @@ static RPCHelpMan getblock()
                         {RPCResult::Type::OBJ, "", "",
                         {
                             {RPCResult::Type::ELISION, "", "The transactions in the format of the getrawtransaction RPC. Different from verbosity = 1 \"tx\" result"},
-                            {RPCResult::Type::NUM, "fee", "The transaction fee in " + CURRENCY_UNIT + ", omitted if block undo data is not available"},
+                            {RPCResult::Type::NUM, "fee", /*optional=*/true, "The transaction fee in " + CURRENCY_UNIT + ", omitted if block undo data is not available"},
                         }},
                     }},
                 }},