diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 6bf41d7ba8..e3cf7f3717 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -458,16 +458,16 @@ static RPCHelpMan getdifficulty()
 
 static std::vector<RPCResult> MempoolEntryDescription() { return {
     RPCResult{RPCResult::Type::NUM, "vsize", "virtual transaction size. This can be different from actual serialized size for high-sigop transactions."},
-    RPCResult{RPCResult::Type::STR_AMOUNT, "fee", "transaction fee in " + CURRENCY_UNIT + " (DEPRECATED)"},
-    RPCResult{RPCResult::Type::STR_AMOUNT, "modifiedfee", "transaction fee with fee deltas used for mining priority (DEPRECATED)"},
+    RPCResult{RPCResult::Type::STR_AMOUNT, "fee", /*optional=*/true, "transaction fee in " + CURRENCY_UNIT + " (DEPRECATED)"},
+    RPCResult{RPCResult::Type::STR_AMOUNT, "modifiedfee", /*optional=*/true, "transaction fee with fee deltas used for mining priority (DEPRECATED)"},
     RPCResult{RPCResult::Type::NUM_TIME, "time", "local time transaction entered pool in " + UNIX_EPOCH_TIME},
     RPCResult{RPCResult::Type::NUM, "height", "block height when transaction entered pool"},
     RPCResult{RPCResult::Type::NUM, "descendantcount", "number of in-mempool descendant transactions (including this one)"},
     RPCResult{RPCResult::Type::NUM, "descendantsize", "size of in-mempool descendants (including this one)"},
-    RPCResult{RPCResult::Type::STR_AMOUNT, "descendantfees", "modified fees (see above) of in-mempool descendants (including this one) (DEPRECATED)"},
+    RPCResult{RPCResult::Type::STR_AMOUNT, "descendantfees",  /*optional=*/true, "modified fees (see above) of in-mempool descendants (including this one) (DEPRECATED)"},
     RPCResult{RPCResult::Type::NUM, "ancestorcount", "number of in-mempool ancestor transactions (including this one)"},
     RPCResult{RPCResult::Type::NUM, "ancestorsize", "size of in-mempool ancestors (including this one)"},
-    RPCResult{RPCResult::Type::STR_AMOUNT, "ancestorfees", "modified fees (see above) of in-mempool ancestors (including this one) (DEPRECATED)"},
+    RPCResult{RPCResult::Type::STR_AMOUNT, "ancestorfees", /*optional=*/true, "modified fees (see above) of in-mempool ancestors (including this one) (DEPRECATED)"},
     RPCResult{RPCResult::Type::OBJ, "fees", "",
     {
         RPCResult{RPCResult::Type::STR_AMOUNT, "base", "transaction fee in " + CURRENCY_UNIT},