diff --git a/src/ripple/app/consensus/RCLValidations.cpp b/src/ripple/app/consensus/RCLValidations.cpp
index 86a3e5207dd..ff007acb2c4 100644
--- a/src/ripple/app/consensus/RCLValidations.cpp
+++ b/src/ripple/app/consensus/RCLValidations.cpp
@@ -198,7 +198,7 @@ handleNewValidation(Application& app,
         {
             auto const seq = val->getFieldU32(sfLedgerSequence);
             dmp(j.warn(),
-                "already validated sequence at or past " + to_string(seq));
+                "already validated sequence at or past " + std::to_string(seq));
         }
 
         if (val->isTrusted() && outcome == ValStatus::current)
diff --git a/src/ripple/app/ledger/impl/InboundLedger.cpp b/src/ripple/app/ledger/impl/InboundLedger.cpp
index ce6e63177d7..266695aaf56 100644
--- a/src/ripple/app/ledger/impl/InboundLedger.cpp
+++ b/src/ripple/app/ledger/impl/InboundLedger.cpp
@@ -208,7 +208,7 @@ InboundLedger::~InboundLedger ()
             "Acquire " << mHash << " abort " <<
             ((getTimeouts () == 0) ? std::string() :
                 (std::string ("timeouts:") +
-                to_string (getTimeouts ()) + " ")) <<
+                 std::to_string (getTimeouts ()) + " ")) <<
             mStats.get ();
     }
 }
@@ -463,7 +463,7 @@ void InboundLedger::done ()
         (mFailed ? " fail " : " ") <<
         ((getTimeouts () == 0) ? std::string() :
             (std::string ("timeouts:") +
-            to_string (getTimeouts ()) + " ")) <<
+             std::to_string (getTimeouts ()) + " ")) <<
         mStats.get ();
 
     assert (mComplete || mFailed);
diff --git a/src/ripple/app/misc/impl/TxQ.cpp b/src/ripple/app/misc/impl/TxQ.cpp
index da4e57e5761..7f0500f4d42 100644
--- a/src/ripple/app/misc/impl/TxQ.cpp
+++ b/src/ripple/app/misc/impl/TxQ.cpp
@@ -958,7 +958,7 @@ TxQ::apply(Application& app, OpenView& view,
                 auto const potentialTotalSpend = multiTxn->fee +
                     std::min(balance - std::min(balance, reserve),
                     multiTxn->potentialSpend);
-                assert(potentialTotalSpend > 0);
+                assert(potentialTotalSpend > XRPAmount{0});
                 sleBump->setFieldAmount(sfBalance,
                     balance - potentialTotalSpend);
                 sleBump->setFieldU32(sfSequence, tSeq);
@@ -1516,11 +1516,11 @@ TxQ::doRPC(Application& app) const
     auto& levels = ret[jss::levels] = Json::objectValue;
 
     ret[jss::ledger_current_index] = view->info().seq;
-    ret[jss::expected_ledger_size] = to_string(metrics.txPerLedger);
-    ret[jss::current_ledger_size] = to_string(metrics.txInLedger);
-    ret[jss::current_queue_size] = to_string(metrics.txCount);
+    ret[jss::expected_ledger_size] = std::to_string(metrics.txPerLedger);
+    ret[jss::current_ledger_size] = std::to_string(metrics.txInLedger);
+    ret[jss::current_queue_size] = std::to_string(metrics.txCount);
     if (metrics.txQMaxSize)
-        ret[jss::max_queue_size] = to_string(*metrics.txQMaxSize);
+        ret[jss::max_queue_size] = std::to_string(*metrics.txQMaxSize);
 
     levels[jss::reference_level] = to_string(metrics.referenceFeeLevel);
     levels[jss::minimum_level] = to_string(metrics.minProcessingFeeLevel);
diff --git a/src/ripple/app/tx/impl/InvariantCheck.cpp b/src/ripple/app/tx/impl/InvariantCheck.cpp
index f475dfb35d5..3301d5db9a9 100644
--- a/src/ripple/app/tx/impl/InvariantCheck.cpp
+++ b/src/ripple/app/tx/impl/InvariantCheck.cpp
@@ -174,7 +174,7 @@ XRPBalanceChecks::visitEntry(
             return true;
 
         // Can't have a negative balance (0 is OK)
-        if (drops < 0)
+        if (drops < XRPAmount{0})
             return true;
 
         return false;
@@ -262,7 +262,7 @@ NoZeroEscrow::visitEntry(
         if (!amount.native())
             return true;
 
-        if (amount.xrp() <= 0)
+        if (amount.xrp() <= XRPAmount{0})
             return true;
 
         if (amount.xrp() >= INITIAL_XRP)
diff --git a/src/ripple/basics/XRPAmount.h b/src/ripple/basics/XRPAmount.h
index ba38479f2e1..fefab4fb22d 100644
--- a/src/ripple/basics/XRPAmount.h
+++ b/src/ripple/basics/XRPAmount.h
@@ -75,6 +75,7 @@ class XRPAmount
     }
 
     constexpr
+    explicit
     XRPAmount (value_type drops)
         : drops_ (drops)
     {
diff --git a/src/ripple/protocol/STAmount.h b/src/ripple/protocol/STAmount.h
index f8994bcc705..95ee41bd7d5 100644
--- a/src/ripple/protocol/STAmount.h
+++ b/src/ripple/protocol/STAmount.h
@@ -105,6 +105,7 @@ class STAmount
     STAmount (SField const& name, Issue const& issue,
         std::uint64_t mantissa = 0, int exponent = 0, bool negative = false);
 
+    explicit
     STAmount (std::uint64_t mantissa = 0, bool negative = false);
 
     STAmount (Issue const& issue, std::uint64_t mantissa = 0, int exponent = 0,
diff --git a/src/ripple/protocol/SystemParameters.h b/src/ripple/protocol/SystemParameters.h
index ed07733063c..6e96467c3af 100644
--- a/src/ripple/protocol/SystemParameters.h
+++ b/src/ripple/protocol/SystemParameters.h
@@ -42,7 +42,7 @@ systemName ()
 /** Number of drops in the genesis account. */
 constexpr
 XRPAmount
-INITIAL_XRP{ 100'000'000'000 * DROPS_PER_XRP };
+INITIAL_XRP{100'000'000'000 * DROPS_PER_XRP };
 
 /** Returns true if the amount does not exceed the initial XRP in existence. */
 inline
diff --git a/src/ripple/rpc/impl/TransactionSign.cpp b/src/ripple/rpc/impl/TransactionSign.cpp
index e393d439708..a3ddb4c671c 100644
--- a/src/ripple/rpc/impl/TransactionSign.cpp
+++ b/src/ripple/rpc/impl/TransactionSign.cpp
@@ -1154,7 +1154,7 @@ Json::Value transactionSubmitMultiSigned (
                 << " field.  Fees must be specified in XRP.";
             return RPC::make_error (rpcINVALID_PARAMS, err.str ());
         }
-        if (fee <= 0)
+        if (fee <= STAmount{0})
         {
             std::ostringstream err;
             err << "Invalid " << sfFee.fieldName
diff --git a/src/test/app/LoadFeeTrack_test.cpp b/src/test/app/LoadFeeTrack_test.cpp
index 0d8495c2fcf..d6368f931ac 100644
--- a/src/test/app/LoadFeeTrack_test.cpp
+++ b/src/test/app/LoadFeeTrack_test.cpp
@@ -41,12 +41,10 @@ class LoadFeeTrack_test : public beast::unit_test::suite
                 return f;
             }();
 
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 0 }, l, fees, false) ==
-                XRPAmount{ 0 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 10000 }, l, fees, false) ==
-                XRPAmount{ 10000 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 1 }, l, fees, false) ==
-                XRPAmount{ 1 });
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{0}, l, fees, false) == XRPAmount{0});
+            BEAST_EXPECT(
+                scaleFeeLoad(FeeUnit64{10000}, l, fees, false) == XRPAmount{10000});
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{1}, l, fees, false) == XRPAmount{1});
         }
         {
             Fees const fees = [&]() {
@@ -58,12 +56,10 @@ class LoadFeeTrack_test : public beast::unit_test::suite
                 return f;
             }();
 
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 0 }, l, fees, false) ==
-                XRPAmount{ 0 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 10000 }, l, fees, false) ==
-                XRPAmount{ 100000 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 1 }, l, fees, false) ==
-                XRPAmount{ 10 });
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{0}, l, fees, false) == XRPAmount{0});
+            BEAST_EXPECT(
+                scaleFeeLoad(FeeUnit64{10000}, l, fees, false) == XRPAmount{100000});
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{1}, l, fees, false) == XRPAmount{10});
         }
         {
             Fees const fees = [&]()
@@ -76,12 +72,10 @@ class LoadFeeTrack_test : public beast::unit_test::suite
                 return f;
             }();
 
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 0 }, l, fees, false) ==
-                XRPAmount{ 0 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 10000 }, l, fees, false) ==
-                XRPAmount{ 1000 });
-            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{ 1 }, l, fees, false) ==
-                XRPAmount{ 0 });
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{0}, l, fees, false) == XRPAmount{0});
+            BEAST_EXPECT(
+                scaleFeeLoad(FeeUnit64{10000}, l, fees, false) == XRPAmount{1000});
+            BEAST_EXPECT(scaleFeeLoad(FeeUnit64{1}, l, fees, false) == XRPAmount{0});
         }
     }
 };
diff --git a/src/test/app/PayChan_test.cpp b/src/test/app/PayChan_test.cpp
index 8842738ae26..0957a8bd783 100644
--- a/src/test/app/PayChan_test.cpp
+++ b/src/test/app/PayChan_test.cpp
@@ -299,7 +299,7 @@ struct PayChan_test : public beast::unit_test::suite
             // Try to claim more than authorized
             auto const preBob = env.balance (bob);
             STAmount const authAmt = chanBal + XRP (500);
-            STAmount const reqAmt = authAmt + 1;
+            STAmount const reqAmt = authAmt + STAmount{1};
             assert (reqAmt <= chanAmt);
             auto const sig =
                 signClaimAuth (alice.pk (), alice.sk (), chan, authAmt);
diff --git a/src/test/app/SHAMapStore_test.cpp b/src/test/app/SHAMapStore_test.cpp
index e2cb94ce0c9..ccd4a5f3829 100644
--- a/src/test/app/SHAMapStore_test.cpp
+++ b/src/test/app/SHAMapStore_test.cpp
@@ -39,7 +39,7 @@ class SHAMapStore_test : public beast::unit_test::suite
     {
         cfg->LEDGER_HISTORY = deleteInterval;
         auto& section = cfg->section(ConfigSection::nodeDatabase());
-        section.set("online_delete", to_string(deleteInterval));
+        section.set("online_delete", std::to_string(deleteInterval));
         return cfg;
     }
 
@@ -182,7 +182,7 @@ class SHAMapStore_test : public beast::unit_test::suite
         store.rendezvous();
 
         auto ledger = env.rpc("ledger", "validated");
-        BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++)));
+        BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++)));
 
         BEAST_EXPECT(store.getLastRotated() == ledgerSeq - 1);
         return ledgerSeq;
@@ -230,19 +230,19 @@ class SHAMapStore_test : public beast::unit_test::suite
 
         for (auto i = firstSeq + 1; i < deleteInterval + firstSeq; ++i)
         {
-            env.fund(XRP(10000), noripple("test" + to_string(i)));
+            env.fund(XRP(10000), noripple("test" + std::to_string(i)));
             env.close();
 
             ledgerTmp = env.rpc("ledger", "current");
-            BEAST_EXPECT(goodLedger(env, ledgerTmp, to_string(i)));
+            BEAST_EXPECT(goodLedger(env, ledgerTmp, std::to_string(i)));
         }
         BEAST_EXPECT(store.getLastRotated() == lastRotated);
 
         for (auto i = 3; i < deleteInterval + lastRotated; ++i)
         {
-            ledgers.emplace(std::make_pair(i,
-                env.rpc("ledger", to_string(i))));
-            BEAST_EXPECT(goodLedger(env, ledgers[i], to_string(i), true) &&
+            ledgers.emplace(
+                std::make_pair(i, env.rpc("ledger", std::to_string(i))));
+            BEAST_EXPECT(goodLedger(env, ledgers[i], std::to_string(i), true) &&
                 getHash(ledgers[i]).length());
         }
 
@@ -255,7 +255,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "current");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(deleteInterval + 4)));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(deleteInterval + 4)));
         }
 
         store.rendezvous();
@@ -275,13 +275,13 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             ledgerTmp = env.rpc("ledger", "current");
-            BEAST_EXPECT(goodLedger(env, ledgerTmp, to_string(i + 3)));
+            BEAST_EXPECT(goodLedger(env, ledgerTmp, std::to_string(i + 3)));
 
-            ledgers.emplace(std::make_pair(i,
-                env.rpc("ledger", to_string(i))));
+            ledgers.emplace(
+                std::make_pair(i, env.rpc("ledger", std::to_string(i))));
             BEAST_EXPECT(store.getLastRotated() == lastRotated ||
                 i == lastRotated + deleteInterval - 2);
-            BEAST_EXPECT(goodLedger(env, ledgers[i], to_string(i), true) &&
+            BEAST_EXPECT(goodLedger(env, ledgers[i], std::to_string(i), true) &&
                 getHash(ledgers[i]).length());
         }
 
@@ -320,7 +320,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -335,7 +335,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++), true));
         }
 
         store.rendezvous();
@@ -351,7 +351,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -389,7 +389,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -398,7 +398,7 @@ class SHAMapStore_test : public beast::unit_test::suite
         BEAST_EXPECT(lastRotated == store.getLastRotated());
 
         // This does not kick off a cleanup
-        canDelete = env.rpc("can_delete", to_string(
+        canDelete = env.rpc("can_delete", std::to_string(
             ledgerSeq + deleteInterval / 2));
         BEAST_EXPECT(!RPC::contains_error(canDelete[jss::result]));
         BEAST_EXPECT(canDelete[jss::result][jss::can_delete] ==
@@ -414,7 +414,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++), true));
         }
 
         store.rendezvous();
@@ -430,7 +430,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -442,7 +442,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++), true));
         }
 
         store.rendezvous();
@@ -464,7 +464,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -476,7 +476,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++), true));
         }
 
         store.rendezvous();
@@ -497,7 +497,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq), true));
         }
 
         store.rendezvous();
@@ -509,7 +509,7 @@ class SHAMapStore_test : public beast::unit_test::suite
             env.close();
 
             auto ledger = env.rpc("ledger", "validated");
-            BEAST_EXPECT(goodLedger(env, ledger, to_string(ledgerSeq++), true));
+            BEAST_EXPECT(goodLedger(env, ledger, std::to_string(ledgerSeq++), true));
         }
 
         store.rendezvous();
diff --git a/src/test/basics/FeeUnits_test.cpp b/src/test/basics/FeeUnits_test.cpp
index 681c149ff00..dab27da2cef 100644
--- a/src/test/basics/FeeUnits_test.cpp
+++ b/src/test/basics/FeeUnits_test.cpp
@@ -344,8 +344,7 @@ class feeunits_test
     void run() override
     {
         BEAST_EXPECT(INITIAL_XRP.drops() == 100'000'000'000'000'000);
-        BEAST_EXPECT(INITIAL_XRP ==
-            XRPAmount{ 100'000'000'000'000'000 });
+        BEAST_EXPECT(INITIAL_XRP == XRPAmount{100'000'000'000'000'000});
 
         testTypes();
         testJson();
diff --git a/src/test/basics/XRPAmount_test.cpp b/src/test/basics/XRPAmount_test.cpp
index 3bca6ec23e5..1cfd52f9bf9 100644
--- a/src/test/basics/XRPAmount_test.cpp
+++ b/src/test/basics/XRPAmount_test.cpp
@@ -132,8 +132,7 @@ class XRPAmount_test : public beast::unit_test::suite
     {
         // Explicitly test every defined function for the XRPAmount class
         // since some of them are templated, but not used anywhere else.
-        auto make = [&](auto x) -> XRPAmount {
-            return x; };
+        auto make = [&](auto x) -> XRPAmount { return XRPAmount{x}; };
 
         XRPAmount defaulted;
         (void)defaulted;
@@ -156,8 +155,8 @@ class XRPAmount_test : public beast::unit_test::suite
         test = make(targetSame);
         BEAST_EXPECT(test.drops() == 200);
         BEAST_EXPECT(test == targetSame);
-        BEAST_EXPECT(test < XRPAmount{ 1000 });
-        BEAST_EXPECT(test > XRPAmount{ 100 });
+        BEAST_EXPECT(test < XRPAmount{1000});
+        BEAST_EXPECT(test > XRPAmount{100});
 
         test = std::int64_t(200);
         BEAST_EXPECT(test.drops() == 200);
diff --git a/src/test/jtx/amount.h b/src/test/jtx/amount.h
index 245c42c5443..c59a15196e5 100644
--- a/src/test/jtx/amount.h
+++ b/src/test/jtx/amount.h
@@ -143,6 +143,14 @@ operator== (PrettyAmount const& lhs,
     return lhs.value() == rhs.value();
 }
 
+inline
+bool
+operator!= (PrettyAmount const& lhs,
+            PrettyAmount const& rhs)
+{
+    return !operator==(lhs, rhs);
+}
+
 std::ostream&
 operator<< (std::ostream& os,
     PrettyAmount const& amount);
diff --git a/src/test/jtx/fee.h b/src/test/jtx/fee.h
index 46792cf6d30..bd347b65148 100644
--- a/src/test/jtx/fee.h
+++ b/src/test/jtx/fee.h
@@ -58,6 +58,12 @@ class fee
                 "fee: not XRP");
     }
 
+    explicit
+    fee(std::uint64_t amount)
+        : fee{STAmount{amount}}
+    {
+    }
+
     void
     operator()(Env&, JTx& jt) const;
 };
diff --git a/src/test/jtx/impl/amount.cpp b/src/test/jtx/impl/amount.cpp
index 16a6450663e..7f958ce797b 100644
--- a/src/test/jtx/impl/amount.cpp
+++ b/src/test/jtx/impl/amount.cpp
@@ -77,7 +77,7 @@ operator<< (std::ostream& os,
     if (amount.value().native())
     {
         // measure in hundredths
-        XRPAmount const c{dropsPerXRP.drops() / 100};
+        auto const c = dropsPerXRP.drops() / 100;
         auto const n = amount.value().mantissa();
         if(n < c)
         {
diff --git a/src/test/jtx/impl/envconfig.cpp b/src/test/jtx/impl/envconfig.cpp
index 626b056c059..04e50e433ba 100644
--- a/src/test/jtx/impl/envconfig.cpp
+++ b/src/test/jtx/impl/envconfig.cpp
@@ -35,9 +35,9 @@ std::atomic<bool> envUseIPv4 {false};
 void
 setupConfigForUnitTests (Config& cfg)
 {
-    std::string const port_peer = to_string(port_base);
-    std::string port_rpc = to_string(port_base + 1);
-    std::string port_ws = to_string(port_base + 2);
+    std::string const port_peer = std::to_string(port_base);
+    std::string port_rpc = std::to_string(port_base + 1);
+    std::string port_ws = std::to_string(port_base + 2);
 
     cfg.overwrite (ConfigSection::nodeDatabase (), "type", "memory");
     cfg.overwrite (ConfigSection::nodeDatabase (), "path", "main");
diff --git a/src/test/ledger/Invariants_test.cpp b/src/test/ledger/Invariants_test.cpp
index 6ba629ca1d8..7cb100267ad 100644
--- a/src/test/ledger/Invariants_test.cpp
+++ b/src/test/ledger/Invariants_test.cpp
@@ -137,7 +137,7 @@ class Invariants_test : public beast::unit_test::suite
                 if(! sle)
                     return false;
                 auto amt = sle->getFieldAmount (sfBalance);
-                sle->setFieldAmount (sfBalance, amt + 500);
+                sle->setFieldAmount (sfBalance, amt + STAmount{500});
                 ac.view().update (sle);
                 return true;
             });
@@ -299,7 +299,7 @@ class Invariants_test : public beast::unit_test::suite
                 auto const sle = ac.view().peek (keylet::account(A1.id()));
                 if(! sle)
                     return false;
-                sle->setFieldAmount (sfBalance, {1, true});
+                sle->setFieldAmount (sfBalance, STAmount{1, true});
                 BEAST_EXPECT(sle->getFieldAmount(sfBalance).negative());
                 ac.view().update (sle);
                 return true;
@@ -328,9 +328,10 @@ class Invariants_test : public beast::unit_test::suite
             [](Account const&, Account const&, ApplyContext&) { return true; },
             XRPAmount{INITIAL_XRP});
 
-         doInvariantCheck (enabled,
-            {{ "fee paid is 20 exceeds fee specified in transaction." },
-             { "XRP net change of 0 doesn't match fee 20" }},
+        doInvariantCheck(
+            enabled,
+            {{"fee paid is 20 exceeds fee specified in transaction."},
+             {"XRP net change of 0 doesn't match fee 20"}},
             [](Account const&, Account const&, ApplyContext&) { return true; },
             XRPAmount{20},
             STTx { ttACCOUNT_SET,
diff --git a/src/test/protocol/STAmount_test.cpp b/src/test/protocol/STAmount_test.cpp
index df23a1a21f2..ef9c38285e3 100644
--- a/src/test/protocol/STAmount_test.cpp
+++ b/src/test/protocol/STAmount_test.cpp
@@ -78,7 +78,7 @@ class STAmount_test : public beast::unit_test::suite
         STAmount num (noIssue(), n);
         STAmount den (noIssue(), d);
         STAmount mul (noIssue(), m);
-        STAmount quot = divide (n, d, noIssue());
+        STAmount quot = divide(STAmount(n), STAmount(d), noIssue());
         STAmount res = roundSelf (multiply (quot, mul, noIssue()));
 
         BEAST_EXPECT(! res.native ());
diff --git a/src/test/rpc/LedgerRPC_test.cpp b/src/test/rpc/LedgerRPC_test.cpp
index a6f77ba82db..34d992a6541 100644
--- a/src/test/rpc/LedgerRPC_test.cpp
+++ b/src/test/rpc/LedgerRPC_test.cpp
@@ -83,7 +83,7 @@ class LedgerRPC_test : public beast::unit_test::suite
             // using current identifier
             auto const jrr = env.rpc("ledger", "current") [jss::result];
             BEAST_EXPECT(jrr[jss::ledger][jss::closed] == false);
-            BEAST_EXPECT(jrr[jss::ledger][jss::ledger_index] == to_string(env.current()->info().seq));
+            BEAST_EXPECT(jrr[jss::ledger][jss::ledger_index] == std::to_string(env.current()->info().seq));
             BEAST_EXPECT(jrr[jss::ledger_current_index] == env.current()->info().seq);
         }
     }
diff --git a/src/test/rpc/Subscribe_test.cpp b/src/test/rpc/Subscribe_test.cpp
index 284ce4dc5e7..c5dee3c23b1 100644
--- a/src/test/rpc/Subscribe_test.cpp
+++ b/src/test/rpc/Subscribe_test.cpp
@@ -370,7 +370,7 @@ class Subscribe_test : public beast::unit_test::suite
                         jv[jss::ledger_hash] ==
                             to_string(env.closed()->info().hash) &&
                         jv[jss::ledger_index] ==
-                            to_string(env.closed()->info().seq) &&
+                            std::to_string(env.closed()->info().seq) &&
                         jv[jss::flags] ==
                             (vfFullyCanonicalSig | STValidation::kFullFlag) &&
                         jv[jss::full] == true &&
diff --git a/src/test/rpc/Transaction_test.cpp b/src/test/rpc/Transaction_test.cpp
index de7b167cffd..fa66b8b61b1 100644
--- a/src/test/rpc/Transaction_test.cpp
+++ b/src/test/rpc/Transaction_test.cpp
@@ -35,6 +35,7 @@ class Transaction_test : public beast::unit_test::suite
         testcase("Test Range Request");
 
         using namespace test::jtx;
+        using std::to_string;
 
         const char* COMMAND   = jss::tx.c_str();
         const char* BINARY    = jss::binary.c_str();
diff --git a/src/test/server/ServerStatus_test.cpp b/src/test/server/ServerStatus_test.cpp
index 5fce31950c4..ee940c54c70 100644
--- a/src/test/server/ServerStatus_test.cpp
+++ b/src/test/server/ServerStatus_test.cpp
@@ -593,7 +593,7 @@ class ServerStatus_test :
         using namespace boost::asio;
         using namespace boost::beast::http;
         Env env {*this, envconfig([&](std::unique_ptr<Config> cfg) {
-            (*cfg)["port_rpc"].set("limit", to_string(limit));
+            (*cfg)["port_rpc"].set("limit", std::to_string(limit));
             return cfg;
         })};
 
@@ -612,7 +612,7 @@ class ServerStatus_test :
 
         auto it =
             r.async_resolve(
-                ip::tcp::resolver::query{ip, to_string(port)}, yield[ec]);
+                ip::tcp::resolver::query{ip, std::to_string(port)}, yield[ec]);
         BEAST_EXPECT(! ec);
 
         std::vector<std::pair<ip::tcp::socket, boost::beast::multi_buffer>> clients;
@@ -721,7 +721,7 @@ class ServerStatus_test :
 
         auto it =
             r.async_resolve(
-                ip::tcp::resolver::query{ip, to_string(port)}, yield[ec]);
+                ip::tcp::resolver::query{ip, std::to_string(port)}, yield[ec]);
         if(! BEAST_EXPECT(! ec))
             return;
 
@@ -731,7 +731,7 @@ class ServerStatus_test :
             return;
 
         boost::beast::websocket::stream<boost::asio::ip::tcp::socket&> ws{sock};
-        ws.handshake(ip + ":" + to_string(port), "/");
+        ws.handshake(ip + ":" + std::to_string(port), "/");
 
         // helper lambda, used below
         auto sendAndParse = [&](std::string const& req) -> Json::Value