diff --git a/src/addrdb.h b/src/addrdb.h
--- a/src/addrdb.h
+++ b/src/addrdb.h
@@ -55,7 +55,7 @@
         banReason = BanReasonUnknown;
     }
 
-    std::string banReasonToString() {
+    std::string banReasonToString() const {
         switch (banReason) {
             case BanReasonNodeMisbehaving:
                 return "node misbehaving";
diff --git a/src/dbwrapper.h b/src/dbwrapper.h
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -127,7 +127,7 @@
         : parent(_parent), piter(_piter){};
     ~CDBIterator();
 
-    bool Valid();
+    bool Valid() const;
 
     void SeekToFirst();
 
diff --git a/src/dbwrapper.cpp b/src/dbwrapper.cpp
--- a/src/dbwrapper.cpp
+++ b/src/dbwrapper.cpp
@@ -192,7 +192,7 @@
 CDBIterator::~CDBIterator() {
     delete piter;
 }
-bool CDBIterator::Valid() {
+bool CDBIterator::Valid() const {
     return piter->Valid();
 }
 void CDBIterator::SeekToFirst() {
diff --git a/src/merkleblock.h b/src/merkleblock.h
--- a/src/merkleblock.h
+++ b/src/merkleblock.h
@@ -67,7 +67,7 @@
      * Helper function to efficiently calculate the number of nodes at given
      * height in the merkle tree.
      */
-    unsigned int CalcTreeWidth(int height) {
+    unsigned int CalcTreeWidth(int height) const {
         return (nTransactions + (1 << height) - 1) >> height;
     }
 
diff --git a/src/miner.h b/src/miner.h
--- a/src/miner.h
+++ b/src/miner.h
@@ -206,7 +206,7 @@
     /** Remove confirmed (inBlock) entries from given set */
     void onlyUnconfirmed(CTxMemPool::setEntries &testSet);
     /** Test if a new package would "fit" in the block */
-    bool TestPackage(uint64_t packageSize, int64_t packageSigOpsCost);
+    bool TestPackage(uint64_t packageSize, int64_t packageSigOpsCost) const;
     /** Perform checks on each transaction in a package:
      * locktime, serialized size (if necessary)
      * These checks should always succeed, and they're here
diff --git a/src/miner.cpp b/src/miner.cpp
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -266,7 +266,8 @@
     }
 }
 
-bool BlockAssembler::TestPackage(uint64_t packageSize, int64_t packageSigOps) {
+bool BlockAssembler::TestPackage(uint64_t packageSize,
+                                 int64_t packageSigOps) const {
     auto blockSizeWithPackage = nBlockSize + packageSize;
     if (blockSizeWithPackage >= nMaxGeneratedBlockSize) {
         return false;
diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -225,7 +225,7 @@
     void requestShutdown(Config &config);
 
     /// Get process return value
-    int getReturnValue() { return returnValue; }
+    int getReturnValue() const { return returnValue; }
 
     /// Get window identifier of QMainWindow (BitcoinGUI)
     WId getMainWinId() const;
diff --git a/src/qt/modaloverlay.h b/src/qt/modaloverlay.h
--- a/src/qt/modaloverlay.h
+++ b/src/qt/modaloverlay.h
@@ -33,7 +33,7 @@
     // will show or hide the modal layer
     void showHide(bool hide = false, bool userRequested = false);
     void closeClicked();
-    bool isLayerVisible() { return layerIsVisible; }
+    bool isLayerVisible() const { return layerIsVisible; }
 
 protected:
     bool eventFilter(QObject *obj, QEvent *ev) override;
diff --git a/src/qt/optionsmodel.h b/src/qt/optionsmodel.h
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -61,20 +61,20 @@
     void setDisplayUnit(const QVariant &value);
 
     /* Explicit getters */
-    bool getHideTrayIcon() { return fHideTrayIcon; }
-    bool getMinimizeToTray() { return fMinimizeToTray; }
-    bool getMinimizeOnClose() { return fMinimizeOnClose; }
-    int getDisplayUnit() { return nDisplayUnit; }
-    QString getThirdPartyTxUrls() { return strThirdPartyTxUrls; }
+    bool getHideTrayIcon() const { return fHideTrayIcon; }
+    bool getMinimizeToTray() const { return fMinimizeToTray; }
+    bool getMinimizeOnClose() const { return fMinimizeOnClose; }
+    int getDisplayUnit() const { return nDisplayUnit; }
+    QString getThirdPartyTxUrls() const { return strThirdPartyTxUrls; }
     bool getProxySettings(QNetworkProxy &proxy) const;
-    bool getCoinControlFeatures() { return fCoinControlFeatures; }
+    bool getCoinControlFeatures() const { return fCoinControlFeatures; }
     const QString &getOverriddenByCommandLine() {
         return strOverriddenByCommandLine;
     }
 
     /* Restart flag helper */
     void setRestartRequired(bool fRequired);
-    bool isRestartRequired();
+    bool isRestartRequired() const;
 
 private:
     /* Qt-only settings */
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -507,7 +507,7 @@
     return settings.setValue("fRestartRequired", fRequired);
 }
 
-bool OptionsModel::isRestartRequired() {
+bool OptionsModel::isRestartRequired() const {
     QSettings settings;
     return settings.value("fRestartRequired", false).toBool();
 }
diff --git a/src/qt/transactionrecord.h b/src/qt/transactionrecord.h
--- a/src/qt/transactionrecord.h
+++ b/src/qt/transactionrecord.h
@@ -149,7 +149,7 @@
 
     /** Return whether a status update is needed.
      */
-    bool statusUpdateNeeded();
+    bool statusUpdateNeeded() const;
 };
 
 #endif // BITCOIN_QT_TRANSACTIONRECORD_H
diff --git a/src/qt/transactionrecord.cpp b/src/qt/transactionrecord.cpp
--- a/src/qt/transactionrecord.cpp
+++ b/src/qt/transactionrecord.cpp
@@ -221,7 +221,7 @@
     }
 }
 
-bool TransactionRecord::statusUpdateNeeded() {
+bool TransactionRecord::statusUpdateNeeded() const {
     AssertLockHeld(cs_main);
     return status.cur_num_blocks != chainActive.Height();
 }
diff --git a/src/qt/transactiontablemodel.h b/src/qt/transactiontablemodel.h
--- a/src/qt/transactiontablemodel.h
+++ b/src/qt/transactiontablemodel.h
@@ -83,7 +83,7 @@
                         int role) const override;
     QModelIndex index(int row, int column,
                       const QModelIndex &parent = QModelIndex()) const override;
-    bool processingQueuedTransactions() {
+    bool processingQueuedTransactions() const {
         return fProcessingQueuedTransactions;
     }
 
diff --git a/src/qt/walletmodeltransaction.h b/src/qt/walletmodeltransaction.h
--- a/src/qt/walletmodeltransaction.h
+++ b/src/qt/walletmodeltransaction.h
@@ -22,15 +22,15 @@
         const QList<SendCoinsRecipient> &recipients);
     ~WalletModelTransaction();
 
-    QList<SendCoinsRecipient> getRecipients();
+    QList<SendCoinsRecipient> getRecipients() const;
 
-    CWalletTx *getTransaction();
+    CWalletTx *getTransaction() const;
     unsigned int getTransactionSize();
 
     void setTransactionFee(const Amount newFee);
-    Amount getTransactionFee();
+    Amount getTransactionFee() const;
 
-    Amount getTotalTransactionAmount();
+    Amount getTotalTransactionAmount() const;
 
     void newPossibleKeyChange(CWallet *wallet);
     CReserveKey *getPossibleKeyChange();
diff --git a/src/qt/walletmodeltransaction.cpp b/src/qt/walletmodeltransaction.cpp
--- a/src/qt/walletmodeltransaction.cpp
+++ b/src/qt/walletmodeltransaction.cpp
@@ -18,11 +18,11 @@
     delete walletTransaction;
 }
 
-QList<SendCoinsRecipient> WalletModelTransaction::getRecipients() {
+QList<SendCoinsRecipient> WalletModelTransaction::getRecipients() const {
     return recipients;
 }
 
-CWalletTx *WalletModelTransaction::getTransaction() {
+CWalletTx *WalletModelTransaction::getTransaction() const {
     return walletTransaction;
 }
 
@@ -31,7 +31,7 @@
                               : CTransaction(*walletTransaction).GetTotalSize();
 }
 
-Amount WalletModelTransaction::getTransactionFee() {
+Amount WalletModelTransaction::getTransactionFee() const {
     return fee;
 }
 
@@ -72,7 +72,7 @@
     }
 }
 
-Amount WalletModelTransaction::getTotalTransactionAmount() {
+Amount WalletModelTransaction::getTotalTransactionAmount() const {
     Amount totalTransactionAmount = Amount::zero();
     for (const SendCoinsRecipient &rcp : recipients) {
         totalTransactionAmount += rcp.amount;
diff --git a/src/scheduler.h b/src/scheduler.h
--- a/src/scheduler.h
+++ b/src/scheduler.h
@@ -84,7 +84,7 @@
     int nThreadsServicingQueue;
     bool stopRequested;
     bool stopWhenEmpty;
-    bool shouldStop() {
+    bool shouldStop() const {
         return stopRequested || (stopWhenEmpty && taskQueue.empty());
     }
 };
diff --git a/src/streams.h b/src/streams.h
--- a/src/streams.h
+++ b/src/streams.h
@@ -310,7 +310,7 @@
     //
     bool eof() const { return size() == 0; }
     CDataStream *rdbuf() { return this; }
-    int in_avail() { return size(); }
+    int in_avail() const { return size(); }
 
     void SetType(int n) { nType = n; }
     int GetType() const { return nType; }
@@ -608,7 +608,7 @@
     }
 
     // return the current reading position
-    uint64_t GetPos() { return nReadPos; }
+    uint64_t GetPos() const { return nReadPos; }
 
     // rewind to a given reading position
     bool SetPos(uint64_t nPos) {
diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -92,8 +92,8 @@
         BOOST_CHECK_EQUAL(DynamicMemoryUsage(), ret);
     }
 
-    CCoinsMap &map() { return cacheCoins; }
-    size_t &usage() { return cachedCoinsUsage; }
+    CCoinsMap &map() const { return cacheCoins; }
+    size_t &usage() const { return cachedCoinsUsage; }
 };
 } // namespace
 
diff --git a/src/test/prevector_tests.cpp b/src/test/prevector_tests.cpp
--- a/src/test/prevector_tests.cpp
+++ b/src/test/prevector_tests.cpp
@@ -148,9 +148,9 @@
         pre_vector.assign(n, value);
     }
 
-    Size size() { return real_vector.size(); }
+    Size size() const { return real_vector.size(); }
 
-    Size capacity() { return pre_vector.capacity(); }
+    Size capacity() const { return pre_vector.capacity(); }
 
     void shrink_to_fit() {
         pre_vector.shrink_to_fit();
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -413,7 +413,7 @@
         return array;
     }
 
-    std::string GetComment() { return comment; }
+    std::string GetComment() const { return comment; }
 };
 
 std::string JSONPrettyPrint(const UniValue &univalue) {
diff --git a/src/txmempool.h b/src/txmempool.h
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -726,7 +726,7 @@
         return mapTx.size();
     }
 
-    uint64_t GetTotalTxSize() {
+    uint64_t GetTotalTxSize() const {
         LOCK(cs);
         return totalTxSize;
     }
diff --git a/src/wallet/db.h b/src/wallet/db.h
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -45,7 +45,7 @@
     void Reset();
 
     void MakeMock();
-    bool IsMock() { return fMockDb; }
+    bool IsMock() const { return fMockDb; }
 
     /**
      * Verify that database file strFile is OK. If it is not, call the callback