diff --git a/src/addrdb.h b/src/addrdb.h
index 6cb36dfac4e60..8105ebc9b3dda 100644
--- a/src/addrdb.h
+++ b/src/addrdb.h
@@ -61,7 +61,7 @@ class CBanEntry
         banReason = BanReasonUnknown;
     }
 
-    std::string banReasonToString()
+    std::string banReasonToString() const
     {
         switch (banReason) {
         case BanReasonNodeMisbehaving:
diff --git a/src/dbwrapper.cpp b/src/dbwrapper.cpp
index 3e72c5bb9b80b..72eeeef2c3db8 100644
--- a/src/dbwrapper.cpp
+++ b/src/dbwrapper.cpp
@@ -190,7 +190,7 @@ bool CDBWrapper::IsEmpty()
 }
 
 CDBIterator::~CDBIterator() { delete piter; }
-bool CDBIterator::Valid() { return piter->Valid(); }
+bool CDBIterator::Valid() const { return piter->Valid(); }
 void CDBIterator::SeekToFirst() { piter->SeekToFirst(); }
 void CDBIterator::Next() { piter->Next(); }
 
diff --git a/src/dbwrapper.h b/src/dbwrapper.h
index 7575d207ae5a4..54092f9f597a4 100644
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -130,7 +130,7 @@ class CDBIterator
         parent(_parent), piter(_piter) { };
     ~CDBIterator();
 
-    bool Valid();
+    bool Valid() const;
 
     void SeekToFirst();
 
diff --git a/src/merkleblock.h b/src/merkleblock.h
index f590c487dee0f..20f2b368860ed 100644
--- a/src/merkleblock.h
+++ b/src/merkleblock.h
@@ -63,7 +63,7 @@ class CPartialMerkleTree
     bool fBad;
 
     /** 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.cpp b/src/miner.cpp
index 403d3d4e4a9f7..f1942ec57045b 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -224,7 +224,7 @@ void BlockAssembler::onlyUnconfirmed(CTxMemPool::setEntries& testSet)
     }
 }
 
-bool BlockAssembler::TestPackage(uint64_t packageSize, int64_t packageSigOpsCost)
+bool BlockAssembler::TestPackage(uint64_t packageSize, int64_t packageSigOpsCost) const
 {
     // TODO: switch to weight-based accounting for packages instead of vsize-based accounting.
     if (nBlockWeight + WITNESS_SCALE_FACTOR * packageSize >= nBlockMaxWeight)
diff --git a/src/miner.h b/src/miner.h
index 5c9cfd78f0444..685b4e0cc8dd7 100644
--- a/src/miner.h
+++ b/src/miner.h
@@ -187,7 +187,7 @@ class BlockAssembler
     /** 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, premature-witness, serialized size (if necessary)
       * These checks should always succeed, and they're here
diff --git a/src/qt/bitcoin.cpp b/src/qt/bitcoin.cpp
index 2b6bd354a0968..3fd58a2f9a0e7 100644
--- a/src/qt/bitcoin.cpp
+++ b/src/qt/bitcoin.cpp
@@ -227,7 +227,7 @@ class BitcoinApplication: public QApplication
     void requestShutdown();
 
     /// 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
index 21ccdbd8397e2..cda23f9540e89 100644
--- a/src/qt/modaloverlay.h
+++ b/src/qt/modaloverlay.h
@@ -32,7 +32,7 @@ public Q_SLOTS:
     // 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);
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index 77efef3e3ca26..e9960a01b13d0 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -441,7 +441,7 @@ void OptionsModel::setRestartRequired(bool fRequired)
     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/optionsmodel.h b/src/qt/optionsmodel.h
index 78529fbdcc921..0ac82a4148b41 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -59,18 +59,18 @@ class OptionsModel : public QAbstractListModel
     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/transactionrecord.cpp b/src/qt/transactionrecord.cpp
index 2ece0d0f289bb..36d98ce49d0f9 100644
--- a/src/qt/transactionrecord.cpp
+++ b/src/qt/transactionrecord.cpp
@@ -248,7 +248,7 @@ void TransactionRecord::updateStatus(const CWalletTx &wtx)
     status.needsUpdate = false;
 }
 
-bool TransactionRecord::statusUpdateNeeded()
+bool TransactionRecord::statusUpdateNeeded() const
 {
     AssertLockHeld(cs_main);
     return status.cur_num_blocks != chainActive.Height() || status.needsUpdate;
diff --git a/src/qt/transactionrecord.h b/src/qt/transactionrecord.h
index 59f681224fc99..a26e676142531 100644
--- a/src/qt/transactionrecord.h
+++ b/src/qt/transactionrecord.h
@@ -140,7 +140,7 @@ class TransactionRecord
 
     /** Return whether a status update is needed.
      */
-    bool statusUpdateNeeded();
+    bool statusUpdateNeeded() const;
 };
 
 #endif // BITCOIN_QT_TRANSACTIONRECORD_H
diff --git a/src/qt/transactiontablemodel.h b/src/qt/transactiontablemodel.h
index 80aeb64c41d1e..b1f81498b2c2e 100644
--- a/src/qt/transactiontablemodel.h
+++ b/src/qt/transactiontablemodel.h
@@ -79,7 +79,7 @@ class TransactionTableModel : public QAbstractTableModel
     QVariant data(const QModelIndex &index, int role) const;
     QVariant headerData(int section, Qt::Orientation orientation, int role) const;
     QModelIndex index(int row, int column, const QModelIndex & parent = QModelIndex()) const;
-    bool processingQueuedTransactions() { return fProcessingQueuedTransactions; }
+    bool processingQueuedTransactions() const { return fProcessingQueuedTransactions; }
 
 private:
     CWallet* wallet;
diff --git a/src/qt/walletmodeltransaction.cpp b/src/qt/walletmodeltransaction.cpp
index 8bc9ef725e4d9..eae2c27f8a491 100644
--- a/src/qt/walletmodeltransaction.cpp
+++ b/src/qt/walletmodeltransaction.cpp
@@ -22,12 +22,12 @@ WalletModelTransaction::~WalletModelTransaction()
     delete walletTransaction;
 }
 
-QList<SendCoinsRecipient> WalletModelTransaction::getRecipients()
+QList<SendCoinsRecipient> WalletModelTransaction::getRecipients() const
 {
     return recipients;
 }
 
-CWalletTx *WalletModelTransaction::getTransaction()
+CWalletTx *WalletModelTransaction::getTransaction() const
 {
     return walletTransaction;
 }
@@ -37,7 +37,7 @@ unsigned int WalletModelTransaction::getTransactionSize()
     return (!walletTransaction ? 0 : ::GetVirtualTransactionSize(*walletTransaction));
 }
 
-CAmount WalletModelTransaction::getTransactionFee()
+CAmount WalletModelTransaction::getTransactionFee() const
 {
     return fee;
 }
@@ -79,7 +79,7 @@ void WalletModelTransaction::reassignAmounts(int nChangePosRet)
     }
 }
 
-CAmount WalletModelTransaction::getTotalTransactionAmount()
+CAmount WalletModelTransaction::getTotalTransactionAmount() const
 {
     CAmount totalTransactionAmount = 0;
     for (const SendCoinsRecipient &rcp : recipients)
diff --git a/src/qt/walletmodeltransaction.h b/src/qt/walletmodeltransaction.h
index 64922efada5e5..d7ecd7aa8cdf6 100644
--- a/src/qt/walletmodeltransaction.h
+++ b/src/qt/walletmodeltransaction.h
@@ -22,15 +22,15 @@ class WalletModelTransaction
     explicit WalletModelTransaction(const QList<SendCoinsRecipient> &recipients);
     ~WalletModelTransaction();
 
-    QList<SendCoinsRecipient> getRecipients();
+    QList<SendCoinsRecipient> getRecipients() const;
 
-    CWalletTx *getTransaction();
+    CWalletTx *getTransaction() const;
     unsigned int getTransactionSize();
 
     void setTransactionFee(const CAmount& newFee);
-    CAmount getTransactionFee();
+    CAmount getTransactionFee() const;
 
-    CAmount getTotalTransactionAmount();
+    CAmount getTotalTransactionAmount() const;
 
     void newPossibleKeyChange(CWallet *wallet);
     CReserveKey *getPossibleKeyChange();
diff --git a/src/scheduler.h b/src/scheduler.h
index 0365d668b209b..cc2f01f2ffafe 100644
--- a/src/scheduler.h
+++ b/src/scheduler.h
@@ -81,7 +81,7 @@ class CScheduler
     int nThreadsServicingQueue;
     bool stopRequested;
     bool stopWhenEmpty;
-    bool shouldStop() { return stopRequested || (stopWhenEmpty && taskQueue.empty()); }
+    bool shouldStop() const { return stopRequested || (stopWhenEmpty && taskQueue.empty()); }
 };
 
 /**
diff --git a/src/streams.h b/src/streams.h
index a9668b68bcb17..a3fc919714a9c 100644
--- a/src/streams.h
+++ b/src/streams.h
@@ -332,7 +332,7 @@ class CDataStream
     //
     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; }
@@ -648,7 +648,7 @@ class CBufferedFile
     }
 
     // return the current reading position
-    uint64_t GetPos() {
+    uint64_t GetPos() const {
         return nReadPos;
     }
 
diff --git a/src/sync.h b/src/sync.h
index 4921aedf3993c..ddaf62b3b34c6 100644
--- a/src/sync.h
+++ b/src/sync.h
@@ -280,7 +280,7 @@ class CSemaphoreGrant
         Release();
     }
 
-    operator bool()
+    operator bool() const
     {
         return fHaveGrant;
     }
diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index 99d0277b7cebb..37ddf83f5ebd7 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -89,8 +89,8 @@ class CCoinsViewCacheTest : public CCoinsViewCache
         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
index 345c4a2148c91..841282873f175 100644
--- a/src/test/prevector_tests.cpp
+++ b/src/test/prevector_tests.cpp
@@ -152,11 +152,11 @@ class prevector_tester {
         pre_vector.assign(n, value);
     }
 
-    Size size() {
+    Size size() const {
         return real_vector.size();
     }
 
-    Size capacity() {
+    Size capacity() const {
         return pre_vector.capacity();
     }
 
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index 06b8274f2d67b..17374edcc4b57 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -450,7 +450,7 @@ class TestBuilder
         return array;
     }
 
-    std::string GetComment()
+    std::string GetComment() const
     {
         return comment;
     }
diff --git a/src/txmempool.h b/src/txmempool.h
index 6723ea8e6cafc..0b183cbd90113 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -606,7 +606,7 @@ class CTxMemPool
         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
index 3614e34fbba85..6f3cfe9557042 100644
--- a/src/wallet/db.h
+++ b/src/wallet/db.h
@@ -45,7 +45,7 @@ class CDBEnv
     void Reset();
 
     void MakeMock();
-    bool IsMock() { return fMockDb; }
+    bool IsMock() const { return fMockDb; }
 
     /**
      * Verify that database file strFile is OK. If it is not,