diff --git a/src/crypto/aes.cpp b/src/crypto/aes.cpp
--- a/src/crypto/aes.cpp
+++ b/src/crypto/aes.cpp
@@ -101,7 +101,6 @@
 template <typename T>
 static int CBCDecrypt(const T &dec, const uint8_t iv[AES_BLOCKSIZE],
                       const uint8_t *data, int size, bool pad, uint8_t *out) {
-    uint8_t padsize = 0;
     int written = 0;
     bool fail = false;
     const uint8_t *prev = iv;
@@ -123,7 +122,7 @@
     if (pad) {
         // If used, padding size is the value of the last decrypted byte. For
         // it to be valid, It must be between 1 and AES_BLOCKSIZE.
-        padsize = *--out;
+        uint8_t padsize = *--out;
         fail = !padsize | (padsize > AES_BLOCKSIZE);
 
         // If not well-formed, treat it as though there's no padding.
diff --git a/src/qt/coincontroltreewidget.cpp b/src/qt/coincontroltreewidget.cpp
--- a/src/qt/coincontroltreewidget.cpp
+++ b/src/qt/coincontroltreewidget.cpp
@@ -13,13 +13,14 @@
     if (event->key() == Qt::Key_Space) // press spacebar -> select checkbox
     {
         event->ignore();
-        int COLUMN_CHECKBOX = 0;
-        if (this->currentItem())
+        if (this->currentItem()) {
+            int COLUMN_CHECKBOX = 0;
             this->currentItem()->setCheckState(
                 COLUMN_CHECKBOX, ((this->currentItem()->checkState(
                                        COLUMN_CHECKBOX) == Qt::Checked)
                                       ? Qt::Unchecked
                                       : Qt::Checked));
+        }
     } else if (event->key() == Qt::Key_Escape) // press esc -> close dialog
     {
         event->ignore();
diff --git a/src/qt/recentrequeststablemodel.cpp b/src/qt/recentrequeststablemodel.cpp
--- a/src/qt/recentrequeststablemodel.cpp
+++ b/src/qt/recentrequeststablemodel.cpp
@@ -49,9 +49,8 @@
                                         int role) const {
     if (!index.isValid() || index.row() >= list.length()) return QVariant();
 
-    const RecentRequestEntry *rec = &list[index.row()];
-
     if (role == Qt::DisplayRole || role == Qt::EditRole) {
+        const RecentRequestEntry *rec = &list[index.row()];
         switch (index.column()) {
             case Date:
                 return GUIUtil::dateTimeStr(rec->date);
diff --git a/src/qt/trafficgraphwidget.cpp b/src/qt/trafficgraphwidget.cpp
--- a/src/qt/trafficgraphwidget.cpp
+++ b/src/qt/trafficgraphwidget.cpp
@@ -38,13 +38,14 @@
 }
 
 void TrafficGraphWidget::paintPath(QPainterPath &path, QQueue<float> &samples) {
-    int h = height() - YMARGIN * 2, w = width() - XMARGIN * 2;
-    int sampleCount = samples.size(), x = XMARGIN + w, y;
+    int sampleCount = samples.size();
     if (sampleCount > 0) {
+        int h = height() - YMARGIN * 2, w = width() - XMARGIN * 2;
+        int x = XMARGIN + w;
         path.moveTo(x, YMARGIN + h);
         for (int i = 0; i < sampleCount; ++i) {
             x = XMARGIN + w - w * i / DESIRED_SAMPLES;
-            y = YMARGIN + h - (int)(h * samples.at(i) / fMax);
+            int y = YMARGIN + h - (int)(h * samples.at(i) / fMax);
             path.lineTo(x, y);
         }
         path.lineTo(x, YMARGIN + h);
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -116,16 +116,14 @@
                         std::shared_ptr<CReserveScript> coinbaseScript,
                         int nGenerate, uint64_t nMaxTries, bool keepScript) {
     static const int nInnerLoopCount = 0x100000;
-    int nHeightStart = 0;
     int nHeightEnd = 0;
     int nHeight = 0;
 
     {
         // Don't keep cs_main locked.
         LOCK(cs_main);
-        nHeightStart = chainActive.Height();
-        nHeight = nHeightStart;
-        nHeightEnd = nHeightStart + nGenerate;
+        nHeight = chainActive.Height();
+        nHeightEnd = nHeight + nGenerate;
     }
 
     unsigned int nExtraNonce = 0;
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -1316,7 +1316,6 @@
     CTransactionRef tx(MakeTransactionRef(std::move(mtx)));
     const uint256 &txid = tx->GetId();
 
-    bool fLimitFree = false;
     Amount nMaxRawTxFee = maxTxFee;
     if (request.params.size() > 1 && request.params[1].get_bool()) {
         nMaxRawTxFee = Amount::zero();
@@ -1336,6 +1335,7 @@
             // Push to local node and sync with wallets.
             CValidationState state;
             bool fMissingInputs;
+            bool fLimitFree = false;
             if (!AcceptToMemoryPool(config, g_mempool, state, std::move(tx),
                                     fLimitFree, &fMissingInputs, false,
                                     nMaxRawTxFee)) {
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -142,10 +142,9 @@
 bool ProduceSignature(const BaseSignatureCreator &creator,
                       const CScript &fromPubKey, SignatureData &sigdata) {
     CScript script = fromPubKey;
-    bool solved = true;
     std::vector<valtype> result;
     txnouttype whichType;
-    solved = SignStep(creator, script, result, whichType);
+    bool solved = SignStep(creator, script, result, whichType);
     CScript subscript;
 
     if (solved && whichType == TX_SCRIPTHASH) {
diff --git a/src/test/checkqueue_tests.cpp b/src/test/checkqueue_tests.cpp
--- a/src/test/checkqueue_tests.cpp
+++ b/src/test/checkqueue_tests.cpp
@@ -385,11 +385,11 @@
         boost::thread_group tg;
         std::mutex m;
         std::condition_variable cv;
-        bool has_lock{false};
-        bool has_tried{false};
-        bool done{false};
-        bool done_ack{false};
         {
+            bool has_lock{false};
+            bool has_tried{false};
+            bool done{false};
+            bool done_ack{false};
             std::unique_lock<std::mutex> l(m);
             tg.create_thread([&] {
                 CCheckQueueControl<FakeCheck> control(queue.get());
diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -470,7 +470,6 @@
 
 CDB::CDB(CWalletDBWrapper &dbw, const char *pszMode, bool fFlushOnCloseIn)
     : pdb(nullptr), activeTxn(nullptr) {
-    int ret;
     fReadOnly = (!strchr(pszMode, '+') && !strchr(pszMode, 'w'));
     fFlushOnClose = fFlushOnCloseIn;
     env = dbw.env;
@@ -495,6 +494,7 @@
 
         pdb = env->mapDb[strFilename];
         if (pdb == nullptr) {
+            int ret;
             std::unique_ptr<Db> pdb_temp =
                 std::make_unique<Db>(env->dbenv.get(), 0);