diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1562,11 +1562,9 @@
 int64_t CalculateMaximumSignedTxSize(const CTransaction &tx,
                                      const CWallet *wallet, bool use_max_sig) {
     std::vector<CTxOut> txouts;
-    // Look up the inputs.  We should have already checked that this transaction
-    // IsAllFromMe(ISMINE_SPENDABLE), so every input should already be in our
-    // wallet, with a valid index into the vout array, and the ability to sign.
     for (auto &input : tx.vin) {
         const auto mi = wallet->mapWallet.find(input.prevout.GetTxId());
+        // Can not estimate size without knowing the input details
         if (mi == wallet->mapWallet.end()) {
             return -1;
         }
@@ -1583,8 +1581,6 @@
                                      bool use_max_sig) {
     CMutableTransaction txNew(tx);
     if (!wallet->DummySignTx(txNew, txouts, use_max_sig)) {
-        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
-        // implies that we can sign for every input.
         return -1;
     }
     return GetSerializeSize(txNew, PROTOCOL_VERSION);