diff --git a/src/bitcoin-tx.cpp b/src/bitcoin-tx.cpp
index 4fed20865..b36a01b73 100644
--- a/src/bitcoin-tx.cpp
+++ b/src/bitcoin-tx.cpp
@@ -347,7 +347,7 @@ static void MutateTxSign(CMutableTransaction& tx, const string& flagStr)
     UniValue keysObj = registers["privatekeys"];
     fGivenKeys = true;
 
-    for (unsigned int kidx = 0; kidx < keysObj.size(); kidx++) {
+    for (size_t kidx = 0; kidx < keysObj.size(); kidx++) {
         if (!keysObj[kidx].isStr())
             throw runtime_error("privatekey not a string");
         CBitcoinSecret vchSecret;
@@ -364,7 +364,7 @@ static void MutateTxSign(CMutableTransaction& tx, const string& flagStr)
         throw runtime_error("prevtxs register variable must be set.");
     UniValue prevtxsObj = registers["prevtxs"];
     {
-        for (unsigned int previdx = 0; previdx < prevtxsObj.size(); previdx++) {
+        for (size_t previdx = 0; previdx < prevtxsObj.size(); previdx++) {
             UniValue prevOut = prevtxsObj[previdx];
             if (!prevOut.isObject())
                 throw runtime_error("expected prevtxs internal object");
diff --git a/src/rpcrawtransaction.cpp b/src/rpcrawtransaction.cpp
index 597da3763..a23c1d8ee 100644
--- a/src/rpcrawtransaction.cpp
+++ b/src/rpcrawtransaction.cpp
@@ -306,7 +306,7 @@ UniValue gettxoutproof(const UniValue& params, bool fHelp)
     set<uint256> setTxids;
     uint256 oneTxid;
     UniValue txids = params[0].get_array();
-    for (unsigned int idx = 0; idx < txids.size(); idx++) {
+    for (size_t idx = 0; idx < txids.size(); idx++) {
         const UniValue& txid = txids[idx];
         if (txid.get_str().length() != 64 || !IsHex(txid.get_str()))
             throw JSONRPCError(RPC_INVALID_PARAMETER, string("Invalid txid ")+txid.get_str());
@@ -436,7 +436,7 @@ UniValue createrawtransaction(const UniValue& params, bool fHelp)
 
     CMutableTransaction rawTx;
 
-    for (unsigned int idx = 0; idx < inputs.size(); idx++) {
+    for (size_t idx = 0; idx < inputs.size(); idx++) {
         const UniValue& input = inputs[idx];
         const UniValue& o = input.get_obj();
 
@@ -731,7 +731,7 @@ UniValue signrawtransaction(const UniValue& params, bool fHelp)
     if (params.size() > 2 && !params[2].isNull()) {
         fGivenKeys = true;
         UniValue keys = params[2].get_array();
-        for (unsigned int idx = 0; idx < keys.size(); idx++) {
+        for (size_t idx = 0; idx < keys.size(); idx++) {
             UniValue k = keys[idx];
             CBitcoinSecret vchSecret;
             bool fGood = vchSecret.SetString(k.get_str());
@@ -751,7 +751,7 @@ UniValue signrawtransaction(const UniValue& params, bool fHelp)
     // Add previous txouts given in the RPC call:
     if (params.size() > 1 && !params[1].isNull()) {
         UniValue prevTxs = params[1].get_array();
-        for (unsigned int idx = 0; idx < prevTxs.size(); idx++) {
+        for (size_t idx = 0; idx < prevTxs.size(); idx++) {
             const UniValue& p = prevTxs[idx];
             if (!p.isObject())
                 throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "expected object with {\"txid'\",\"vout\",\"scriptPubKey\"}");
diff --git a/src/rpcserver.cpp b/src/rpcserver.cpp
index d5b66471d..6fe41193e 100644
--- a/src/rpcserver.cpp
+++ b/src/rpcserver.cpp
@@ -85,7 +85,7 @@ void RPCTypeCheck(const UniValue& params,
                   const list<UniValue::VType>& typesExpected,
                   bool fAllowNull)
 {
-    unsigned int i = 0;
+    size_t i = 0;
     BOOST_FOREACH(UniValue::VType t, typesExpected)
     {
         if (params.size() <= i)
@@ -928,7 +928,7 @@ static UniValue JSONRPCExecOne(const UniValue& req)
 static string JSONRPCExecBatch(const UniValue& vReq)
 {
     UniValue ret(UniValue::VARR);
-    for (unsigned int reqIdx = 0; reqIdx < vReq.size(); reqIdx++)
+    for (size_t reqIdx = 0; reqIdx < vReq.size(); reqIdx++)
         ret.push_back(JSONRPCExecOne(vReq[reqIdx]));
 
     return ret.write() + "\n";
diff --git a/src/test/base58_tests.cpp b/src/test/base58_tests.cpp
index 9e74f5f42..bd754cafe 100644
--- a/src/test/base58_tests.cpp
+++ b/src/test/base58_tests.cpp
@@ -28,7 +28,7 @@ BOOST_FIXTURE_TEST_SUITE(base58_tests, BasicTestingSetup)
 BOOST_AUTO_TEST_CASE(base58_EncodeBase58)
 {
     UniValue tests = read_json(std::string(json_tests::base58_encode_decode, json_tests::base58_encode_decode + sizeof(json_tests::base58_encode_decode)));
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 2) // Allow for extra stuff (useful for comments)
@@ -50,7 +50,7 @@ BOOST_AUTO_TEST_CASE(base58_DecodeBase58)
     UniValue tests = read_json(std::string(json_tests::base58_encode_decode, json_tests::base58_encode_decode + sizeof(json_tests::base58_encode_decode)));
     std::vector<unsigned char> result;
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 2) // Allow for extra stuff (useful for comments)
@@ -126,7 +126,7 @@ BOOST_AUTO_TEST_CASE(base58_keys_valid_parse)
     CBitcoinAddress addr;
     SelectParams(CBaseChainParams::MAIN);
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 3) // Allow for extra stuff (useful for comments)
@@ -181,7 +181,7 @@ BOOST_AUTO_TEST_CASE(base58_keys_valid_gen)
     UniValue tests = read_json(std::string(json_tests::base58_keys_valid, json_tests::base58_keys_valid + sizeof(json_tests::base58_keys_valid)));
     std::vector<unsigned char> result;
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 3) // Allow for extra stuff (useful for comments)
@@ -251,7 +251,7 @@ BOOST_AUTO_TEST_CASE(base58_keys_invalid)
     CBitcoinSecret secret;
     CBitcoinAddress addr;
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 1) // Allow for extra stuff (useful for comments)
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index 02cd878d8..dfb4c2f65 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -583,11 +583,11 @@ BOOST_AUTO_TEST_CASE(script_build)
         UniValue json_good = read_json(std::string(json_tests::script_valid, json_tests::script_valid + sizeof(json_tests::script_valid)));
         UniValue json_bad = read_json(std::string(json_tests::script_invalid, json_tests::script_invalid + sizeof(json_tests::script_invalid)));
 
-        for (unsigned int idx = 0; idx < json_good.size(); idx++) {
+        for (size_t idx = 0; idx < json_good.size(); idx++) {
             const UniValue& tv = json_good[idx];
             tests_good.insert(tv.get_array().write());
         }
-        for (unsigned int idx = 0; idx < json_bad.size(); idx++) {
+        for (size_t idx = 0; idx < json_bad.size(); idx++) {
             const UniValue& tv = json_bad[idx];
             tests_bad.insert(tv.get_array().write());
         }
@@ -636,7 +636,7 @@ BOOST_AUTO_TEST_CASE(script_valid)
     // scripts.
     UniValue tests = read_json(std::string(json_tests::script_valid, json_tests::script_valid + sizeof(json_tests::script_valid)));
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         string strTest = test.write();
         if (test.size() < 3) // Allow size > 3; extra stuff ignored (useful for comments)
@@ -661,7 +661,7 @@ BOOST_AUTO_TEST_CASE(script_invalid)
     // Scripts that should evaluate as invalid
     UniValue tests = read_json(std::string(json_tests::script_invalid, json_tests::script_invalid + sizeof(json_tests::script_invalid)));
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         string strTest = test.write();
         if (test.size() < 3) // Allow size > 2; extra stuff ignored (useful for comments)
diff --git a/src/test/sighash_tests.cpp b/src/test/sighash_tests.cpp
index 9b3a82557..ce554ee3e 100644
--- a/src/test/sighash_tests.cpp
+++ b/src/test/sighash_tests.cpp
@@ -205,7 +205,7 @@ BOOST_AUTO_TEST_CASE(sighash_from_data)
 {
     UniValue tests = read_json(std::string(json_tests::sighash, json_tests::sighash + sizeof(json_tests::sighash)));
 
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         std::string strTest = test.write();
         if (test.size() < 1) // Allow for extra stuff (useful for comments)
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index 514982980..d2e9a3388 100644
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -101,7 +101,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
 
     auto verifier = libzcash::ProofVerifier::Strict();
     ScriptError err;
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         string strTest = test.write();
         if (test[0].isArray())
@@ -115,7 +115,7 @@ BOOST_AUTO_TEST_CASE(tx_valid)
             map<COutPoint, CScript> mapprevOutScriptPubKeys;
             UniValue inputs = test[0].get_array();
             bool fValid = true;
-	    for (unsigned int inpIdx = 0; inpIdx < inputs.size(); inpIdx++) {
+            for (size_t inpIdx = 0; inpIdx < inputs.size(); inpIdx++) {
 	        const UniValue& input = inputs[inpIdx];
                 if (!input.isArray())
                 {
@@ -177,7 +177,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
 
     auto verifier = libzcash::ProofVerifier::Strict();
     ScriptError err;
-    for (unsigned int idx = 0; idx < tests.size(); idx++) {
+    for (size_t idx = 0; idx < tests.size(); idx++) {
         UniValue test = tests[idx];
         string strTest = test.write();
         if (test[0].isArray())
@@ -191,7 +191,7 @@ BOOST_AUTO_TEST_CASE(tx_invalid)
             map<COutPoint, CScript> mapprevOutScriptPubKeys;
             UniValue inputs = test[0].get_array();
             bool fValid = true;
-	    for (unsigned int inpIdx = 0; inpIdx < inputs.size(); inpIdx++) {
+	    for (size_t inpIdx = 0; inpIdx < inputs.size(); inpIdx++) {
 	        const UniValue& input = inputs[inpIdx];
                 if (!input.isArray())
                 {
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 90b6d04fa..5e1efe2db 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -1005,7 +1005,7 @@ UniValue sendmany(const UniValue& params, bool fHelp)
         totalAmount += nAmount;
 
         bool fSubtractFeeFromAmount = false;
-        for (unsigned int idx = 0; idx < subtractFeeFromAmount.size(); idx++) {
+        for (size_t idx = 0; idx < subtractFeeFromAmount.size(); idx++) {
             const UniValue& addr = subtractFeeFromAmount[idx];
             if (addr.get_str() == name_)
                 fSubtractFeeFromAmount = true;
@@ -2130,7 +2130,7 @@ UniValue lockunspent(const UniValue& params, bool fHelp)
     }
 
     UniValue outputs = params[1].get_array();
-    for (unsigned int idx = 0; idx < outputs.size(); idx++) {
+    for (size_t idx = 0; idx < outputs.size(); idx++) {
         const UniValue& output = outputs[idx];
         if (!output.isObject())
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected object");
@@ -2354,7 +2354,7 @@ UniValue listunspent(const UniValue& params, bool fHelp)
     set<CBitcoinAddress> setAddress;
     if (params.size() > 2) {
         UniValue inputs = params[2].get_array();
-        for (unsigned int idx = 0; idx < inputs.size(); idx++) {
+        for (size_t idx = 0; idx < inputs.size(); idx++) {
             const UniValue& input = inputs[idx];
             CBitcoinAddress address(input.get_str());
             if (!address.IsValid())