diff --git a/src/wallet/coincontrol.h b/src/wallet/coincontrol.h
index 85cbec76b7..c989512d3e 100644
--- a/src/wallet/coincontrol.h
+++ b/src/wallet/coincontrol.h
@@ -9,9 +9,14 @@
 #include <policy/feerate.h>
 #include <policy/fees.h>
 #include <primitives/transaction.h>
+#include <script/keyorigin.h>
+#include <script/signingprovider.h>
 #include <script/standard.h>
 
 #include <optional>
+#include <algorithm>
+#include <map>
+#include <set>
 
 const int DEFAULT_MIN_DEPTH = 0;
 const int DEFAULT_MAX_DEPTH = 9999999;
@@ -53,6 +58,8 @@ public:
     int m_min_depth = DEFAULT_MIN_DEPTH;
     //! Maximum chain depth value for coin availability
     int m_max_depth = DEFAULT_MAX_DEPTH;
+    //! SigningProvider that has pubkeys and scripts to do spend size estimation for external inputs
+    FlatSigningProvider m_external_provider;
 
     CCoinControl();
 
@@ -66,11 +73,32 @@ public:
         return (setSelected.count(output) > 0);
     }
 
+    bool IsExternalSelected(const COutPoint& output) const
+    {
+        return (m_external_txouts.count(output) > 0);
+    }
+
+    bool GetExternalOutput(const COutPoint& outpoint, CTxOut& txout) const
+    {
+        const auto ext_it = m_external_txouts.find(outpoint);
+        if (ext_it == m_external_txouts.end()) {
+            return false;
+        }
+        txout = ext_it->second;
+        return true;
+    }
+
     void Select(const COutPoint& output)
     {
         setSelected.insert(output);
     }
 
+    void Select(const COutPoint& outpoint, const CTxOut& txout)
+    {
+        setSelected.insert(outpoint);
+        m_external_txouts.emplace(outpoint, txout);
+    }
+
     void UnSelect(const COutPoint& output)
     {
         setSelected.erase(output);
@@ -88,6 +116,7 @@ public:
 
 private:
     std::set<COutPoint> setSelected;
+    std::map<COutPoint, CTxOut> m_external_txouts;
 };
 
 #endif // BITCOIN_WALLET_COINCONTROL_H
diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 1724375f4c..43fcc0416d 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -5,6 +5,7 @@
 #include <consensus/validation.h>
 #include <interfaces/chain.h>
 #include <policy/policy.h>
+#include <script/signingprovider.h>
 #include <util/check.h>
 #include <util/fees.h>
 #include <util/moneystr.h>
@@ -31,21 +32,27 @@ std::string COutput::ToString() const
     return strprintf("COutput(%s, %d, %d) [%s]", tx->GetHash().ToString(), i, nDepth, FormatMoney(tx->tx->vout[i].nValue));
 }
 
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const SigningProvider* provider, bool use_max_sig)
 {
     CMutableTransaction txn;
     txn.vin.push_back(CTxIn(COutPoint()));
-    if (!wallet->DummySignInput(txn.vin[0], txout, use_max_sig)) {
+    if (!provider || !DummySignInput(*provider, txn.vin[0], txout, use_max_sig)) {
         return -1;
     }
     return GetVirtualTransactionInputSize(txn.vin[0]);
 }
 
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
+{
+    const std::unique_ptr<SigningProvider> provider = wallet->GetSolvingProvider(txout.scriptPubKey);
+    return CalculateMaximumSignedInputSize(txout, provider.get(), use_max_sig);
+}
+
 // txouts needs to be in the order of tx.vin
-TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, bool use_max_sig)
+TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control)
 {
     CMutableTransaction txNew(tx);
-    if (!wallet->DummySignTx(txNew, txouts, use_max_sig)) {
+    if (!wallet->DummySignTx(txNew, txouts, coin_control)) {
         return TxSize{-1, -1};
     }
     CTransaction ctx(txNew);
@@ -54,19 +61,27 @@ TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *walle
     return TxSize{vsize, weight};
 }
 
-TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, bool use_max_sig)
+TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const CCoinControl* coin_control)
 {
     std::vector<CTxOut> txouts;
+    // Look up the inputs. The inputs are either in the wallet, or in coin_control.
     for (const CTxIn& input : tx.vin) {
         const auto mi = wallet->mapWallet.find(input.prevout.hash);
         // Can not estimate size without knowing the input details
-        if (mi == wallet->mapWallet.end()) {
+        if (mi != wallet->mapWallet.end()) {
+            assert(input.prevout.n < mi->second.tx->vout.size());
+            txouts.emplace_back(mi->second.tx->vout.at(input.prevout.n));
+        } else if (coin_control) {
+            CTxOut txout;
+            if (!coin_control->GetExternalOutput(input.prevout, txout)) {
+                return TxSize{-1, -1};
+            }
+            txouts.emplace_back(txout);
+        } else {
             return TxSize{-1, -1};
         }
-        assert(input.prevout.n < mi->second.tx->vout.size());
-        txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
     }
-    return CalculateMaximumSignedTxSize(tx, wallet, txouts, use_max_sig);
+    return CalculateMaximumSignedTxSize(tx, wallet, txouts, coin_control);
 }
 
 void AvailableCoins(const CWallet& wallet, std::vector<COutput>& vCoins, const CCoinControl* coinControl, const CAmount& nMinimumAmount, const CAmount& nMaximumAmount, const CAmount& nMinimumSumAmount, const uint64_t nMaximumCount)
@@ -435,32 +450,40 @@ bool SelectCoins(const CWallet& wallet, const std::vector<COutput>& vAvailableCo
 
     std::vector<COutPoint> vPresetInputs;
     coin_control.ListSelected(vPresetInputs);
-    for (const COutPoint& outpoint : vPresetInputs)
-    {
+    for (const COutPoint& outpoint : vPresetInputs) {
+        int input_bytes = -1;
+        CTxOut txout;
         std::map<uint256, CWalletTx>::const_iterator it = wallet.mapWallet.find(outpoint.hash);
-        if (it != wallet.mapWallet.end())
-        {
+        if (it != wallet.mapWallet.end()) {
             const CWalletTx& wtx = it->second;
             // Clearly invalid input, fail
             if (wtx.tx->vout.size() <= outpoint.n) {
                 return false;
             }
-            // Just to calculate the marginal byte size
-            CInputCoin coin(wtx.tx, outpoint.n, GetTxSpendSize(wallet, wtx, outpoint.n, false));
-            nValueFromPresetInputs += coin.txout.nValue;
-            if (coin.m_input_bytes <= 0) {
-                return false; // Not solvable, can't estimate size for fee
-            }
-            coin.effective_value = coin.txout.nValue - coin_selection_params.m_effective_feerate.GetFee(coin.m_input_bytes);
-            if (coin_selection_params.m_subtract_fee_outputs) {
-                value_to_select -= coin.txout.nValue;
-            } else {
-                value_to_select -= coin.effective_value;
-            }
-            setPresetCoins.insert(coin);
-        } else {
-            return false; // TODO: Allow non-wallet inputs
+            input_bytes = GetTxSpendSize(wallet, wtx, outpoint.n, false);
+            txout = wtx.tx->vout.at(outpoint.n);
         }
+        if (input_bytes == -1) {
+            // The input is external. We either did not find the tx in mapWallet, or we did but couldn't compute the input size with wallet data
+            if (!coin_control.GetExternalOutput(outpoint, txout)) {
+                // Not ours, and we don't have solving data.
+                return false;
+            }
+            input_bytes = CalculateMaximumSignedInputSize(txout, &coin_control.m_external_provider, /* use_max_sig */ true);
+        }
+
+        CInputCoin coin(outpoint, txout, input_bytes);
+        nValueFromPresetInputs += coin.txout.nValue;
+        if (coin.m_input_bytes <= 0) {
+            return false; // Not solvable, can't estimate size for fee
+        }
+        coin.effective_value = coin.txout.nValue - coin_selection_params.m_effective_feerate.GetFee(coin.m_input_bytes);
+        if (coin_selection_params.m_subtract_fee_outputs) {
+            value_to_select -= coin.txout.nValue;
+        } else {
+            value_to_select -= coin.effective_value;
+        }
+        setPresetCoins.insert(coin);
     }
 
     // remove preset inputs from vCoins so that Coin Selection doesn't pick them.
@@ -788,10 +811,10 @@ static bool CreateTransactionInternal(
     }
 
     // Calculate the transaction fee
-    TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, coin_control.fAllowWatchOnly);
+    TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
     int nBytes = tx_sizes.vsize;
     if (nBytes < 0) {
-        error = _("Signing transaction failed");
+        error = _("Missing solving data for estimating transaction size");
         return false;
     }
     nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
@@ -813,7 +836,7 @@ static bool CreateTransactionInternal(
         txNew.vout.erase(change_position);
 
         // Because we have dropped this change, the tx size and required fee will be different, so let's recalculate those
-        tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, coin_control.fAllowWatchOnly);
+        tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
         nBytes = tx_sizes.vsize;
         fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes);
     }
diff --git a/src/wallet/spend.h b/src/wallet/spend.h
index e39f134dc3..3a723d9832 100644
--- a/src/wallet/spend.h
+++ b/src/wallet/spend.h
@@ -66,6 +66,7 @@ public:
 
 //Get the marginal bytes of spending the specified output
 int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet, bool use_max_sig = false);
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const SigningProvider* pwallet, bool use_max_sig = false);
 
 struct TxSize {
     int64_t vsize{-1};
@@ -76,8 +77,8 @@ struct TxSize {
 * Use DummySignatureCreator, which inserts 71 byte signatures everywhere.
 * NOTE: this requires that all inputs must be in mapWallet (eg the tx should
 * be AllInputsMine). */
-TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const std::vector<CTxOut>& txouts, bool use_max_sig = false);
-TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, bool use_max_sig = false) EXCLUSIVE_LOCKS_REQUIRED(wallet->cs_wallet);
+TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control = nullptr);
+TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const CCoinControl* coin_control = nullptr) EXCLUSIVE_LOCKS_REQUIRED(wallet->cs_wallet);
 
 /**
  * populate vCoins with vector of available COutputs.
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 6885499be2..2900fb7f93 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1448,19 +1448,13 @@ bool CWallet::AddWalletFlags(uint64_t flags)
 
 // Helper for producing a max-sized low-S low-R signature (eg 71 bytes)
 // or a max-sized low-S signature (e.g. 72 bytes) if use_max_sig is true
-bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout, bool use_max_sig) const
+bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, bool use_max_sig)
 {
     // Fill in dummy signatures for fee calculation.
     const CScript& scriptPubKey = txout.scriptPubKey;
     SignatureData sigdata;
 
-    std::unique_ptr<SigningProvider> provider = GetSolvingProvider(scriptPubKey);
-    if (!provider) {
-        // We don't know about this scriptpbuKey;
-        return false;
-    }
-
-    if (!ProduceSignature(*provider, use_max_sig ? DUMMY_MAXIMUM_SIGNATURE_CREATOR : DUMMY_SIGNATURE_CREATOR, scriptPubKey, sigdata)) {
+    if (!ProduceSignature(provider, use_max_sig ? DUMMY_MAXIMUM_SIGNATURE_CREATOR : DUMMY_SIGNATURE_CREATOR, scriptPubKey, sigdata)) {
         return false;
     }
     UpdateInput(tx_in, sigdata);
@@ -1468,14 +1462,21 @@ bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout, bool use_max_sig
 }
 
 // Helper for producing a bunch of max-sized low-S low-R signatures (eg 71 bytes)
-bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, bool use_max_sig) const
+bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, const CCoinControl* coin_control) const
 {
     // Fill in dummy signatures for fee calculation.
     int nIn = 0;
     for (const auto& txout : txouts)
     {
-        if (!DummySignInput(txNew.vin[nIn], txout, use_max_sig)) {
-            return false;
+        CTxIn& txin = txNew.vin[nIn];
+        // Use max sig if watch only inputs were used or if this particular input is an external input
+        // to ensure a sufficient fee is attained for the requested feerate.
+        const bool use_max_sig = coin_control && (coin_control->fAllowWatchOnly || coin_control->IsExternalSelected(txin.prevout));
+        const std::unique_ptr<SigningProvider> provider = GetSolvingProvider(txout.scriptPubKey);
+        if (!provider || !DummySignInput(*provider, txin, txout, use_max_sig)) {
+            if (!coin_control || !DummySignInput(coin_control->m_external_provider, txin, txout, use_max_sig)) {
+                return false;
+            }
         }
 
         nIn++;
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 15a5933424..0624e00859 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -576,14 +576,13 @@ public:
     /** Pass this transaction to node for mempool insertion and relay to peers if flag set to true */
     bool SubmitTxMemoryPoolAndRelay(const CWalletTx& wtx, std::string& err_string, bool relay) const;
 
-    bool DummySignTx(CMutableTransaction &txNew, const std::set<CTxOut> &txouts, bool use_max_sig = false) const
+    bool DummySignTx(CMutableTransaction &txNew, const std::set<CTxOut> &txouts, const CCoinControl* coin_control = nullptr) const
     {
         std::vector<CTxOut> v_txouts(txouts.size());
         std::copy(txouts.begin(), txouts.end(), v_txouts.begin());
-        return DummySignTx(txNew, v_txouts, use_max_sig);
+        return DummySignTx(txNew, v_txouts, coin_control);
     }
-    bool DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, bool use_max_sig = false) const;
-    bool DummySignInput(CTxIn &tx_in, const CTxOut &txout, bool use_max_sig = false) const;
+    bool DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, const CCoinControl* coin_control = nullptr) const;
 
     bool ImportScripts(const std::set<CScript> scripts, int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
     bool ImportPrivKeys(const std::map<CKeyID, CKey>& privkey_map, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
@@ -928,4 +927,6 @@ bool AddWalletSetting(interfaces::Chain& chain, const std::string& wallet_name);
 //! Remove wallet name from persistent configuration so it will not be loaded on startup.
 bool RemoveWalletSetting(interfaces::Chain& chain, const std::string& wallet_name);
 
+bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, bool use_max_sig);
+
 #endif // BITCOIN_WALLET_WALLET_H