diff --git a/src/coins.h b/src/coins.h
--- a/src/coins.h
+++ b/src/coins.h
@@ -15,7 +15,6 @@
 
 #include <cassert>
 #include <cstdint>
-
 #include <unordered_map>
 
 /**
@@ -198,11 +197,11 @@
     CCoinsViewCache(CCoinsView *baseIn);
 
     // Standard CCoinsView methods
-    bool GetCoin(const COutPoint &outpoint, Coin &coin) const;
-    bool HaveCoin(const COutPoint &outpoint) const;
-    uint256 GetBestBlock() const;
+    bool GetCoin(const COutPoint &outpoint, Coin &coin) const override;
+    bool HaveCoin(const COutPoint &outpoint) const override;
+    uint256 GetBestBlock() const override;
     void SetBestBlock(const uint256 &hashBlock);
-    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
+    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override;
 
     /**
      * Check if we have the given utxo already loaded in this cache.
diff --git a/src/httprpc.cpp b/src/httprpc.cpp
--- a/src/httprpc.cpp
+++ b/src/httprpc.cpp
@@ -18,10 +18,10 @@
 #include "utilstrencodings.h"
 #include "utilstrencodings.h"
 
-#include <cstdio>
-
 #include <boost/algorithm/string.hpp> // boost::trim
 
+#include <cstdio>
+
 /** WWW-Authenticate to present with 401 Unauthorized response */
 static const char *WWW_AUTH_HEADER_DATA = "Basic realm=\"jsonrpc\"";
 
@@ -46,8 +46,9 @@
 class HTTPRPCTimerInterface : public RPCTimerInterface {
 public:
     HTTPRPCTimerInterface(struct event_base *_base) : base(_base) {}
-    const char *Name() { return "HTTP"; }
-    RPCTimerBase *NewTimer(std::function<void(void)> &func, int64_t millis) {
+    const char *Name() override { return "HTTP"; }
+    RPCTimerBase *NewTimer(std::function<void(void)> &func,
+                           int64_t millis) override {
         return new HTTPRPCTimer(base, func, millis);
     }
 
diff --git a/src/httpserver.cpp b/src/httpserver.cpp
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -12,11 +12,6 @@
 #include "ui_interface.h"
 #include "util.h"
 
-#include <cstdio>
-#include <cstdlib>
-#include <cstring>
-
-#include <future>
 #include <signal.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -35,6 +30,11 @@
 #endif
 #endif
 
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <future>
+
 /** Maximum size of http request (request line + headers) */
 static const size_t MAX_HEADERS_SIZE = 8192;
 
@@ -45,7 +45,7 @@
                  const std::string &_path, const HTTPRequestHandler &_func)
         : req(std::move(_req)), path(_path), func(_func), config(&_config) {}
 
-    void operator()() { func(*config, req.get(), path); }
+    void operator()() override { func(*config, req.get(), path); }
 
     std::unique_ptr<HTTPRequest> req;
 
diff --git a/src/init.cpp b/src/init.cpp
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -144,7 +144,7 @@
 class CCoinsViewErrorCatcher : public CCoinsViewBacked {
 public:
     CCoinsViewErrorCatcher(CCoinsView *view) : CCoinsViewBacked(view) {}
-    bool GetCoin(const COutPoint &outpoint, Coin &coin) const {
+    bool GetCoin(const COutPoint &outpoint, Coin &coin) const override {
         try {
             return CCoinsViewBacked::GetCoin(outpoint, coin);
         } catch (const std::runtime_error &e) {
diff --git a/src/keystore.h b/src/keystore.h
--- a/src/keystore.h
+++ b/src/keystore.h
@@ -63,9 +63,9 @@
     WatchOnlySet setWatchOnly;
 
 public:
-    bool AddKeyPubKey(const CKey &key, const CPubKey &pubkey);
-    bool GetPubKey(const CKeyID &address, CPubKey &vchPubKeyOut) const;
-    bool HaveKey(const CKeyID &address) const {
+    bool AddKeyPubKey(const CKey &key, const CPubKey &pubkey) override;
+    bool GetPubKey(const CKeyID &address, CPubKey &vchPubKeyOut) const override;
+    bool HaveKey(const CKeyID &address) const override {
         bool result;
         {
             LOCK(cs_KeyStore);
@@ -73,7 +73,7 @@
         }
         return result;
     }
-    void GetKeys(std::set<CKeyID> &setAddress) const {
+    void GetKeys(std::set<CKeyID> &setAddress) const override {
         setAddress.clear();
         {
             LOCK(cs_KeyStore);
@@ -84,7 +84,7 @@
             }
         }
     }
-    bool GetKey(const CKeyID &address, CKey &keyOut) const {
+    bool GetKey(const CKeyID &address, CKey &keyOut) const override {
         {
             LOCK(cs_KeyStore);
             KeyMap::const_iterator mi = mapKeys.find(address);
@@ -95,15 +95,15 @@
         }
         return false;
     }
-    virtual bool AddCScript(const CScript &redeemScript);
-    virtual bool HaveCScript(const CScriptID &hash) const;
+    virtual bool AddCScript(const CScript &redeemScript) override;
+    virtual bool HaveCScript(const CScriptID &hash) const override;
     virtual bool GetCScript(const CScriptID &hash,
-                            CScript &redeemScriptOut) const;
+                            CScript &redeemScriptOut) const override;
 
-    virtual bool AddWatchOnly(const CScript &dest);
-    virtual bool RemoveWatchOnly(const CScript &dest);
-    virtual bool HaveWatchOnly(const CScript &dest) const;
-    virtual bool HaveWatchOnly() const;
+    virtual bool AddWatchOnly(const CScript &dest) override;
+    virtual bool RemoveWatchOnly(const CScript &dest) override;
+    virtual bool HaveWatchOnly(const CScript &dest) const override;
+    virtual bool HaveWatchOnly() const override;
 };
 
 typedef std::vector<uint8_t, secure_allocator<uint8_t>> CKeyingMaterial;
diff --git a/src/net_processing.h b/src/net_processing.h
--- a/src/net_processing.h
+++ b/src/net_processing.h
@@ -35,14 +35,16 @@
     PeerLogicValidation(CConnman *connmanIn);
 
     virtual void SyncTransaction(const CTransaction &tx,
-                                 const CBlockIndex *pindex, int nPosInBlock);
+                                 const CBlockIndex *pindex,
+                                 int nPosInBlock) override;
     virtual void UpdatedBlockTip(const CBlockIndex *pindexNew,
                                  const CBlockIndex *pindexFork,
-                                 bool fInitialDownload);
+                                 bool fInitialDownload) override;
     virtual void BlockChecked(const CBlock &block,
-                              const CValidationState &state);
-    virtual void NewPoWValidBlock(const CBlockIndex *pindex,
-                                  const std::shared_ptr<const CBlock> &pblock);
+                              const CValidationState &state) override;
+    virtual void
+    NewPoWValidBlock(const CBlockIndex *pindex,
+                     const std::shared_ptr<const CBlock> &pblock) override;
 };
 
 struct CNodeStateStats {
diff --git a/src/qt/bitcoinaddressvalidator.h b/src/qt/bitcoinaddressvalidator.h
--- a/src/qt/bitcoinaddressvalidator.h
+++ b/src/qt/bitcoinaddressvalidator.h
@@ -19,7 +19,7 @@
     explicit BitcoinAddressEntryValidator(const std::string &cashaddrprefix,
                                           QObject *parent);
 
-    State validate(QString &input, int &pos) const;
+    State validate(QString &input, int &pos) const override;
 
 private:
     std::string cashaddrprefix;
@@ -33,7 +33,7 @@
 public:
     explicit BitcoinAddressCheckValidator(QObject *parent);
 
-    State validate(QString &input, int &pos) const;
+    State validate(QString &input, int &pos) const override;
 };
 
 #endif // BITCOIN_QT_BITCOINADDRESSVALIDATOR_H
diff --git a/src/qt/bitcoinamountfield.cpp b/src/qt/bitcoinamountfield.cpp
--- a/src/qt/bitcoinamountfield.cpp
+++ b/src/qt/bitcoinamountfield.cpp
@@ -31,8 +31,10 @@
                 SIGNAL(valueChanged()));
     }
 
-    QValidator::State validate(QString &text, int &pos) const {
-        if (text.isEmpty()) return QValidator::Intermediate;
+    QValidator::State validate(QString &text, int &pos) const override {
+        if (text.isEmpty()) {
+            return QValidator::Intermediate;
+        }
         bool valid = false;
         parse(text, &valid);
         // Make sure we return Intermediate so that fixup() is called on
@@ -40,7 +42,7 @@
         return valid ? QValidator::Intermediate : QValidator::Invalid;
     }
 
-    void fixup(QString &input) const {
+    void fixup(QString &input) const override {
         bool valid = false;
         CAmount val = parse(input, &valid);
         if (valid) {
@@ -60,7 +62,7 @@
         Q_EMIT valueChanged();
     }
 
-    void stepBy(int steps) {
+    void stepBy(int steps) override {
         bool valid = false;
         Amount val(value(&valid));
         val = val + steps * singleStep;
@@ -74,15 +76,16 @@
 
         currentUnit = unit;
 
-        if (valid)
+        if (valid) {
             setValue(val.GetSatoshis());
-        else
+        } else {
             clear();
+        }
     }
 
     void setSingleStep(const CAmount &step) { singleStep = step; }
 
-    QSize minimumSizeHint() const {
+    QSize minimumSizeHint() const override {
         if (cachedMinimumSizeHint.isEmpty()) {
             ensurePolished();
 
@@ -149,7 +152,7 @@
     }
 
 protected:
-    bool event(QEvent *event) {
+    bool event(QEvent *event) override {
         if (event->type() == QEvent::KeyPress ||
             event->type() == QEvent::KeyRelease) {
             QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
@@ -164,7 +167,7 @@
         return QAbstractSpinBox::event(event);
     }
 
-    StepEnabled stepEnabled() const {
+    StepEnabled stepEnabled() const override {
         if (isReadOnly()) {
             // Disable steps when AmountSpinBox is read-only.
             return StepNone;
diff --git a/src/qt/bitcoinunits.h b/src/qt/bitcoinunits.h
--- a/src/qt/bitcoinunits.h
+++ b/src/qt/bitcoinunits.h
@@ -101,8 +101,8 @@
         /** Unit identifier */
         UnitRole = Qt::UserRole
     };
-    int rowCount(const QModelIndex &parent) const;
-    QVariant data(const QModelIndex &index, int role) const;
+    int rowCount(const QModelIndex &parent) const override;
+    QVariant data(const QModelIndex &index, int role) const override;
     ///@}
 
     static QString removeSpaces(QString text) {
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -841,7 +841,7 @@
 
 protected:
     virtual void BlockChecked(const CBlock &block,
-                              const CValidationState &stateIn) {
+                              const CValidationState &stateIn) override {
         if (block.GetHash() != hash) {
             return;
         }
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -166,9 +166,9 @@
         : txTo(txToIn), nIn(nInIn), amount(amountIn), txdata(&txdataIn) {}
     bool CheckSig(const std::vector<uint8_t> &scriptSig,
                   const std::vector<uint8_t> &vchPubKey,
-                  const CScript &scriptCode, uint32_t flags) const;
-    bool CheckLockTime(const CScriptNum &nLockTime) const;
-    bool CheckSequence(const CScriptNum &nSequence) const;
+                  const CScript &scriptCode, uint32_t flags) const override;
+    bool CheckLockTime(const CScriptNum &nLockTime) const override;
+    bool CheckSequence(const CScriptNum &nSequence) const override;
 };
 
 class MutableTransactionSignatureChecker : public TransactionSignatureChecker {
diff --git a/src/script/sigcache.h b/src/script/sigcache.h
--- a/src/script/sigcache.h
+++ b/src/script/sigcache.h
@@ -53,7 +53,7 @@
 
     bool VerifySignature(const std::vector<uint8_t> &vchSig,
                          const CPubKey &vchPubKey,
-                         const uint256 &sighash) const;
+                         const uint256 &sighash) const override;
 };
 
 void InitSignatureCache();
diff --git a/src/script/sign.h b/src/script/sign.h
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -43,9 +43,9 @@
                                 const CTransaction *txToIn, unsigned int nInIn,
                                 const Amount amountIn,
                                 uint32_t nHashTypeIn = SIGHASH_ALL);
-    const BaseSignatureChecker &Checker() const { return checker; }
+    const BaseSignatureChecker &Checker() const override { return checker; }
     bool CreateSig(std::vector<uint8_t> &vchSig, const CKeyID &keyid,
-                   const CScript &scriptCode) const;
+                   const CScript &scriptCode) const override;
 };
 
 class MutableTransactionSignatureCreator : public TransactionSignatureCreator {
@@ -66,9 +66,9 @@
 public:
     DummySignatureCreator(const CKeyStore *keystoreIn)
         : BaseSignatureCreator(keystoreIn) {}
-    const BaseSignatureChecker &Checker() const;
+    const BaseSignatureChecker &Checker() const override;
     bool CreateSig(std::vector<uint8_t> &vchSig, const CKeyID &keyid,
-                   const CScript &scriptCode) const;
+                   const CScript &scriptCode) const override;
 };
 
 struct SignatureData {
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -359,7 +359,7 @@
 
     bool CheckSig(const std::vector<uint8_t> &scriptSig,
                   const std::vector<uint8_t> &vchPubKey,
-                  const CScript &scriptCode, uint32_t flags) const {
+                  const CScript &scriptCode, uint32_t flags) const override {
         return true;
     }
 };
diff --git a/src/support/lockedpool.cpp b/src/support/lockedpool.cpp
--- a/src/support/lockedpool.cpp
+++ b/src/support/lockedpool.cpp
@@ -143,9 +143,9 @@
 class Win32LockedPageAllocator : public LockedPageAllocator {
 public:
     Win32LockedPageAllocator();
-    void *AllocateLocked(size_t len, bool *lockingSuccess);
-    void FreeLocked(void *addr, size_t len);
-    size_t GetLimit();
+    void *AllocateLocked(size_t len, bool *lockingSuccess) override;
+    void FreeLocked(void *addr, size_t len) override;
+    size_t GetLimit() override;
 
 private:
     size_t page_size;
@@ -194,9 +194,9 @@
 class PosixLockedPageAllocator : public LockedPageAllocator {
 public:
     PosixLockedPageAllocator();
-    void *AllocateLocked(size_t len, bool *lockingSuccess);
-    void FreeLocked(void *addr, size_t len);
-    size_t GetLimit();
+    void *AllocateLocked(size_t len, bool *lockingSuccess) override;
+    void FreeLocked(void *addr, size_t len) override;
+    size_t GetLimit() override;
 
 private:
     size_t page_size;
diff --git a/src/test/addrman_tests.cpp b/src/test/addrman_tests.cpp
--- a/src/test/addrman_tests.cpp
+++ b/src/test/addrman_tests.cpp
@@ -22,7 +22,7 @@
         insecure_rand = FastRandomContext(true);
     }
 
-    int RandomInt(int nMax) {
+    int RandomInt(int nMax) override {
         state = (CHashWriter(SER_GETHASH, 0) << state).GetHash().GetCheapHash();
         return (unsigned int)(state % nMax);
     }
diff --git a/src/test/allocator_tests.cpp b/src/test/allocator_tests.cpp
--- a/src/test/allocator_tests.cpp
+++ b/src/test/allocator_tests.cpp
@@ -134,7 +134,7 @@
 public:
     TestLockedPageAllocator(int count_in, int lockedcount_in)
         : count(count_in), lockedcount(lockedcount_in) {}
-    void *AllocateLocked(size_t len, bool *lockingSuccess) {
+    void *AllocateLocked(size_t len, bool *lockingSuccess) override {
         *lockingSuccess = false;
         if (count > 0) {
             --count;
@@ -149,8 +149,8 @@
         }
         return 0;
     }
-    void FreeLocked(void *addr, size_t len) {}
-    size_t GetLimit() { return std::numeric_limits<size_t>::max(); }
+    void FreeLocked(void *addr, size_t len) override {}
+    size_t GetLimit() override { return std::numeric_limits<size_t>::max(); }
 
 private:
     int count;
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
@@ -35,7 +35,7 @@
     std::map<COutPoint, Coin> map_;
 
 public:
-    bool GetCoin(const COutPoint &outpoint, Coin &coin) const {
+    bool GetCoin(const COutPoint &outpoint, Coin &coin) const override {
         std::map<COutPoint, Coin>::const_iterator it = map_.find(outpoint);
         if (it == map_.end()) {
             return false;
@@ -48,14 +48,14 @@
         return true;
     }
 
-    bool HaveCoin(const COutPoint &outpoint) const {
+    bool HaveCoin(const COutPoint &outpoint) const override {
         Coin coin;
         return GetCoin(outpoint, coin);
     }
 
-    uint256 GetBestBlock() const { return hashBestBlock_; }
+    uint256 GetBestBlock() const override { return hashBestBlock_; }
 
-    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
+    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override {
         for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
             if (it->second.flags & CCoinsCacheEntry::DIRTY) {
                 // Same optimization used in CCoinsViewDB is to only write dirty
diff --git a/src/test/net_tests.cpp b/src/test/net_tests.cpp
--- a/src/test/net_tests.cpp
+++ b/src/test/net_tests.cpp
@@ -28,12 +28,12 @@
 
 class CAddrManUncorrupted : public CAddrManSerializationMock {
 public:
-    void Serialize(CDataStream &s) const { CAddrMan::Serialize(s); }
+    void Serialize(CDataStream &s) const override { CAddrMan::Serialize(s); }
 };
 
 class CAddrManCorrupted : public CAddrManSerializationMock {
 public:
-    void Serialize(CDataStream &s) const {
+    void Serialize(CDataStream &s) const override {
         // Produces corrupt output that claims addrman has 20 addrs when it only
         // has one addr.
         uint8_t nVersion = 1;
diff --git a/src/test/versionbits_tests.cpp b/src/test/versionbits_tests.cpp
--- a/src/test/versionbits_tests.cpp
+++ b/src/test/versionbits_tests.cpp
@@ -25,16 +25,18 @@
     mutable ThresholdConditionCache cache;
 
 public:
-    int64_t BeginTime(const Consensus::Params &params) const {
+    int64_t BeginTime(const Consensus::Params &params) const override {
         return TestTime(10000);
     }
-    int64_t EndTime(const Consensus::Params &params) const {
+    int64_t EndTime(const Consensus::Params &params) const override {
         return TestTime(20000);
     }
-    int Period(const Consensus::Params &params) const { return 1000; }
-    int Threshold(const Consensus::Params &params) const { return 900; }
+    int Period(const Consensus::Params &params) const override { return 1000; }
+    int Threshold(const Consensus::Params &params) const override {
+        return 900;
+    }
     bool Condition(const CBlockIndex *pindex,
-                   const Consensus::Params &params) const {
+                   const Consensus::Params &params) const override {
         return (pindex->nVersion & 0x100);
     }
 
diff --git a/src/txdb.h b/src/txdb.h
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -64,7 +64,7 @@
 };
 
 /** CCoinsView backed by the coin database (chainstate/) */
-class CCoinsViewDB : public CCoinsView {
+class CCoinsViewDB final : public CCoinsView {
 protected:
     CDBWrapper db;
 
@@ -88,12 +88,12 @@
 public:
     ~CCoinsViewDBCursor() {}
 
-    bool GetKey(COutPoint &key) const;
-    bool GetValue(Coin &coin) const;
-    unsigned int GetValueSize() const;
+    bool GetKey(COutPoint &key) const override;
+    bool GetValue(Coin &coin) const override;
+    unsigned int GetValueSize() const override;
 
-    bool Valid() const;
-    void Next();
+    bool Valid() const override;
+    void Next() override;
 
 private:
     CCoinsViewDBCursor(CDBIterator *pcursorIn, const uint256 &hashBlockIn)
diff --git a/src/txdb.cpp b/src/txdb.cpp
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -11,10 +11,10 @@
 #include "pow.h"
 #include "uint256.h"
 
-#include <cstdint>
-
 #include <boost/thread.hpp>
 
+#include <cstdint>
+
 static const char DB_COIN = 'C';
 static const char DB_COINS = 'c';
 static const char DB_BLOCK_FILES = 'f';
diff --git a/src/txmempool.h b/src/txmempool.h
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -6,13 +6,6 @@
 #ifndef BITCOIN_TXMEMPOOL_H
 #define BITCOIN_TXMEMPOOL_H
 
-#include <map>
-#include <memory>
-#include <set>
-#include <string>
-#include <utility>
-#include <vector>
-
 #include "amount.h"
 #include "coins.h"
 #include "indirectmap.h"
@@ -25,6 +18,13 @@
 #include <boost/multi_index_container.hpp>
 #include <boost/signals2/signal.hpp>
 
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <utility>
+#include <vector>
+
 class CAutoFile;
 class CBlockIndex;
 class Config;
@@ -795,8 +795,8 @@
 
 public:
     CCoinsViewMemPool(CCoinsView *baseIn, const CTxMemPool &mempoolIn);
-    bool GetCoin(const COutPoint &outpoint, Coin &coin) const;
-    bool HaveCoin(const COutPoint &outpoint) const;
+    bool GetCoin(const COutPoint &outpoint, Coin &coin) const override;
+    bool HaveCoin(const COutPoint &outpoint) const override;
 };
 
 // We want to sort transactions by coin age priority
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1778,19 +1778,21 @@
 public:
     WarningBitsConditionChecker(int bitIn) : bit(bitIn) {}
 
-    int64_t BeginTime(const Consensus::Params &params) const { return 0; }
-    int64_t EndTime(const Consensus::Params &params) const {
+    int64_t BeginTime(const Consensus::Params &params) const override {
+        return 0;
+    }
+    int64_t EndTime(const Consensus::Params &params) const override {
         return std::numeric_limits<int64_t>::max();
     }
-    int Period(const Consensus::Params &params) const {
+    int Period(const Consensus::Params &params) const override {
         return params.nMinerConfirmationWindow;
     }
-    int Threshold(const Consensus::Params &params) const {
+    int Threshold(const Consensus::Params &params) const override {
         return params.nRuleChangeActivationThreshold;
     }
 
     bool Condition(const CBlockIndex *pindex,
-                   const Consensus::Params &params) const {
+                   const Consensus::Params &params) const override {
         return ((pindex->nVersion & VERSIONBITS_TOP_MASK) ==
                 VERSIONBITS_TOP_BITS) &&
                ((pindex->nVersion >> bit) & 1) != 0 &&
diff --git a/src/versionbits.cpp b/src/versionbits.cpp
--- a/src/versionbits.cpp
+++ b/src/versionbits.cpp
@@ -156,21 +156,21 @@
     const Consensus::DeploymentPos id;
 
 protected:
-    int64_t BeginTime(const Consensus::Params &params) const {
+    int64_t BeginTime(const Consensus::Params &params) const override {
         return params.vDeployments[id].nStartTime;
     }
-    int64_t EndTime(const Consensus::Params &params) const {
+    int64_t EndTime(const Consensus::Params &params) const override {
         return params.vDeployments[id].nTimeout;
     }
-    int Period(const Consensus::Params &params) const {
+    int Period(const Consensus::Params &params) const override {
         return params.nMinerConfirmationWindow;
     }
-    int Threshold(const Consensus::Params &params) const {
+    int Threshold(const Consensus::Params &params) const override {
         return params.nRuleChangeActivationThreshold;
     }
 
     bool Condition(const CBlockIndex *pindex,
-                   const Consensus::Params &params) const {
+                   const Consensus::Params &params) const override {
         return (((pindex->nVersion & VERSIONBITS_TOP_MASK) ==
                  VERSIONBITS_TOP_BITS) &&
                 (pindex->nVersion & Mask(params)) != 0);
diff --git a/src/wallet/crypter.h b/src/wallet/crypter.h
--- a/src/wallet/crypter.h
+++ b/src/wallet/crypter.h
@@ -155,18 +155,18 @@
 
     virtual bool AddCryptedKey(const CPubKey &vchPubKey,
                                const std::vector<uint8_t> &vchCryptedSecret);
-    bool AddKeyPubKey(const CKey &key, const CPubKey &pubkey);
-    bool HaveKey(const CKeyID &address) const {
-        {
-            LOCK(cs_KeyStore);
-            if (!IsCrypted()) return CBasicKeyStore::HaveKey(address);
-            return mapCryptedKeys.count(address) > 0;
+    bool AddKeyPubKey(const CKey &key, const CPubKey &pubkey) override;
+    bool HaveKey(const CKeyID &address) const override {
+        LOCK(cs_KeyStore);
+        if (!IsCrypted()) {
+            return CBasicKeyStore::HaveKey(address);
         }
-        return false;
+
+        return mapCryptedKeys.count(address) > 0;
     }
-    bool GetKey(const CKeyID &address, CKey &keyOut) const;
-    bool GetPubKey(const CKeyID &address, CPubKey &vchPubKeyOut) const;
-    void GetKeys(std::set<CKeyID> &setAddress) const {
+    bool GetKey(const CKeyID &address, CKey &keyOut) const override;
+    bool GetPubKey(const CKeyID &address, CPubKey &vchPubKeyOut) const override;
+    void GetKeys(std::set<CKeyID> &setAddress) const override {
         if (!IsCrypted()) {
             CBasicKeyStore::GetKeys(setAddress);
             return;
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -18,6 +18,8 @@
 #include "wallet/rpcwallet.h"
 #include "wallet/walletdb.h"
 
+#include <boost/thread.hpp>
+
 #include <algorithm>
 #include <atomic>
 #include <cstdint>
@@ -28,8 +30,6 @@
 #include <utility>
 #include <vector>
 
-#include <boost/thread.hpp>
-
 extern CWallet *pwalletMain;
 
 /**
@@ -1078,7 +1078,7 @@
     void ReturnKey();
     bool GetReservedKey(CPubKey &pubkey);
     void KeepKey();
-    void KeepScript() { KeepKey(); }
+    void KeepScript() override { KeepKey(); }
 };
 
 /**
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -28,12 +28,12 @@
 #include "wallet/coincontrol.h"
 #include "wallet/finaltx.h"
 
-#include <cassert>
-
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/thread.hpp>
 
+#include <cassert>
+
 CWallet *pwalletMain = nullptr;
 
 /** Transaction fee set by the user */
diff --git a/src/zmq/zmqnotificationinterface.h b/src/zmq/zmqnotificationinterface.h
--- a/src/zmq/zmqnotificationinterface.h
+++ b/src/zmq/zmqnotificationinterface.h
@@ -6,6 +6,7 @@
 #define BITCOIN_ZMQ_ZMQNOTIFICATIONINTERFACE_H
 
 #include "validationinterface.h"
+
 #include <map>
 #include <string>
 
@@ -24,9 +25,10 @@
 
     // CValidationInterface
     void SyncTransaction(const CTransaction &tx, const CBlockIndex *pindex,
-                         int posInBlock);
+                         int posInBlock) override;
     void UpdatedBlockTip(const CBlockIndex *pindexNew,
-                         const CBlockIndex *pindexFork, bool fInitialDownload);
+                         const CBlockIndex *pindexFork,
+                         bool fInitialDownload) override;
 
 private:
     CZMQNotificationInterface();
diff --git a/src/zmq/zmqpublishnotifier.h b/src/zmq/zmqpublishnotifier.h
--- a/src/zmq/zmqpublishnotifier.h
+++ b/src/zmq/zmqpublishnotifier.h
@@ -23,28 +23,28 @@
     */
     bool SendMessage(const char *command, const void *data, size_t size);
 
-    bool Initialize(void *pcontext);
-    void Shutdown();
+    bool Initialize(void *pcontext) override;
+    void Shutdown() override;
 };
 
 class CZMQPublishHashBlockNotifier : public CZMQAbstractPublishNotifier {
 public:
-    bool NotifyBlock(const CBlockIndex *pindex);
+    bool NotifyBlock(const CBlockIndex *pindex) override;
 };
 
 class CZMQPublishHashTransactionNotifier : public CZMQAbstractPublishNotifier {
 public:
-    bool NotifyTransaction(const CTransaction &transaction);
+    bool NotifyTransaction(const CTransaction &transaction) override;
 };
 
 class CZMQPublishRawBlockNotifier : public CZMQAbstractPublishNotifier {
 public:
-    bool NotifyBlock(const CBlockIndex *pindex);
+    bool NotifyBlock(const CBlockIndex *pindex) override;
 };
 
 class CZMQPublishRawTransactionNotifier : public CZMQAbstractPublishNotifier {
 public:
-    bool NotifyTransaction(const CTransaction &transaction);
+    bool NotifyTransaction(const CTransaction &transaction) override;
 };
 
 #endif // BITCOIN_ZMQ_ZMQPUBLISHNOTIFIER_H