diff --git a/src/addrdb.h b/src/addrdb.h
index 4e3b45c3f09504..4a13b29a0fa37f 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 703388a4f87efb..ac2de204028077 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 66efca4e4a4501..670b31289f838e 100644
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -139,7 +139,7 @@ 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 8a974d4aaaea4f..8e1a35e3de38e7 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 4911eaf5ae6b14..68aa079b33f593 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -260,7 +260,7 @@ void BlockAssembler::onlyUnconfirmed(CTxMemPool::setEntries& testSet)
     }
 }
 
-bool BlockAssembler::TestPackage(uint64_t packageSize, unsigned int packageSigOps)
+bool BlockAssembler::TestPackage(uint64_t packageSize, unsigned int packageSigOps) const
 {
     if (nBlockSize + packageSize >= nBlockMaxSize)
         return false;
diff --git a/src/miner.h b/src/miner.h
index 7d64d7f9fa355e..4494d57126fbd7 100644
--- a/src/miner.h
+++ b/src/miner.h
@@ -186,7 +186,7 @@ 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, unsigned int packageSigOps);
+    bool TestPackage(uint64_t packageSize, unsigned int packageSigOps) const;
     /** Perform checks on each transaction in a package:
       * locktime
       * These checks should always succeed, and they're here
diff --git a/src/qt/dash.cpp b/src/qt/dash.cpp
index 99566e93410c71..41be48a1cf614c 100644
--- a/src/qt/dash.cpp
+++ b/src/qt/dash.cpp
@@ -231,7 +231,7 @@ 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 d82983ea7dd4cf..71cdadf410ecd8 100644
--- a/src/qt/modaloverlay.h
+++ b/src/qt/modaloverlay.h
@@ -33,7 +33,7 @@ public Q_SLOTS:
     void showHide(bool hide = false, bool userRequested = false);
     void closeClicked();
     void hideForever();
-    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 155bea8a3a7c70..dc57e7781c0868 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -576,7 +576,7 @@ 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 3dd4ff15167d70..fe80d9fdd4fe80 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -68,19 +68,19 @@ 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; }
     bool getShowAdvancedPSUI() { return fShowAdvancedPSUI; }
     const QString& getOverriddenByCommandLine() { return strOverriddenByCommandLine; }
 
     /* Restart flag helper */
     void setRestartRequired(bool fRequired);
-    bool isRestartRequired();
+    bool isRestartRequired() const;
     bool resetSettings;
 
 private:
diff --git a/src/qt/transactionrecord.cpp b/src/qt/transactionrecord.cpp
index c2d180093e600b..716b9a1ef34666 100644
--- a/src/qt/transactionrecord.cpp
+++ b/src/qt/transactionrecord.cpp
@@ -363,7 +363,7 @@ void TransactionRecord::updateStatus(const CWalletTx &wtx, int chainLockHeight)
     status.needsUpdate = false;
 }
 
-bool TransactionRecord::statusUpdateNeeded(int chainLockHeight)
+bool TransactionRecord::statusUpdateNeeded(int chainLockHeight) 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 309f3fd005f48f..2b6c64c7e93a67 100644
--- a/src/qt/transactionrecord.h
+++ b/src/qt/transactionrecord.h
@@ -166,7 +166,7 @@ class TransactionRecord
 
     /** Return whether a status update is needed.
      */
-    bool statusUpdateNeeded(int chainLockHeight);
+    bool statusUpdateNeeded(int chainLockHeight) const;
 };
 
 #endif // BITCOIN_QT_TRANSACTIONRECORD_H
diff --git a/src/qt/transactiontablemodel.h b/src/qt/transactiontablemodel.h
index 3f2d3a2f4defea..62a8077f2e85a9 100644
--- a/src/qt/transactiontablemodel.h
+++ b/src/qt/transactiontablemodel.h
@@ -86,7 +86,7 @@ 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; }
     void updateChainLockHeight(int chainLockHeight);
     int getChainLockHeight() const;
 
diff --git a/src/qt/walletmodeltransaction.cpp b/src/qt/walletmodeltransaction.cpp
index a8a9feb4d08d86..d11c17ea0d3ee8 100644
--- a/src/qt/walletmodeltransaction.cpp
+++ b/src/qt/walletmodeltransaction.cpp
@@ -21,12 +21,12 @@ WalletModelTransaction::~WalletModelTransaction()
     delete walletTransaction;
 }
 
-QList<SendCoinsRecipient> WalletModelTransaction::getRecipients()
+QList<SendCoinsRecipient> WalletModelTransaction::getRecipients() const
 {
     return recipients;
 }
 
-CWalletTx *WalletModelTransaction::getTransaction()
+CWalletTx *WalletModelTransaction::getTransaction() const
 {
     return walletTransaction;
 }
@@ -36,7 +36,7 @@ unsigned int WalletModelTransaction::getTransactionSize()
     return (!walletTransaction ? 0 : (::GetSerializeSize(walletTransaction->tx, SER_NETWORK, PROTOCOL_VERSION)));
 }
 
-CAmount WalletModelTransaction::getTransactionFee()
+CAmount WalletModelTransaction::getTransactionFee() const
 {
     return fee;
 }
@@ -85,7 +85,7 @@ void WalletModelTransaction::reassignAmounts()
     }
 }
 
-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 e3eabcc2abcc16..c21aec69974723 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 0365d668b209b8..cc2f01f2ffafea 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 88ae1fe740cb49..375d474bc54421 100644
--- a/src/streams.h
+++ b/src/streams.h
@@ -289,7 +289,7 @@ 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; }
@@ -605,7 +605,7 @@ 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 90ae3c9634a8dd..864d427e1cef18 100644
--- a/src/sync.h
+++ b/src/sync.h
@@ -283,7 +283,7 @@ 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 1dee71de46aa52..99c4f7428f1b26 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 4b6a29d9885706..6baab42f1eb742 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 a80644d8ad9141..71565ce5a5797d 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -377,7 +377,7 @@ class TestBuilder
         return array;
     }
 
-    std::string GetComment()
+    std::string GetComment() const
     {
         return comment;
     }
diff --git a/src/txmempool.h b/src/txmempool.h
index e6b90e3481ad7c..123a85d1df9d3f 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -642,7 +642,7 @@ class CTxMemPool
         return mapTx.size();
     }
 
-    uint64_t GetTotalTxSize()
+    uint64_t GetTotalTxSize() const
     {
         LOCK(cs);
         return totalTxSize;