diff --git a/src/rpc/server.cpp b/src/rpc/server.cpp
--- a/src/rpc/server.cpp
+++ b/src/rpc/server.cpp
@@ -28,7 +28,9 @@
 /* Timer-creating functions */
 static RPCTimerInterface *timerInterface = nullptr;
 /* Map of name to timer. */
-static std::map<std::string, std::unique_ptr<RPCTimerBase>> deadlineTimers;
+static Mutex g_deadline_timers_mutex;
+static std::map<std::string, std::unique_ptr<RPCTimerBase>>
+    deadlineTimers GUARDED_BY(g_deadline_timers_mutex);
 static bool ExecuteCommand(Config &config, const CRPCCommand &command,
                            const JSONRPCRequest &request, UniValue &result,
                            bool last_handler);
@@ -346,7 +348,7 @@
 
 void StopRPC() {
     LogPrint(BCLog::RPC, "Stopping RPC\n");
-    deadlineTimers.clear();
+    WITH_LOCK(g_deadline_timers_mutex, deadlineTimers.clear());
     DeleteAuthCookie();
     g_rpcSignals.Stopped();
 }
@@ -543,6 +545,7 @@
         throw JSONRPCError(RPC_INTERNAL_ERROR,
                            "No timer handler registered for RPC");
     }
+    LOCK(g_deadline_timers_mutex);
     deadlineTimers.erase(name);
     LogPrint(BCLog::RPC, "queue run of timer %s in %i seconds (using %s)\n",
              name, nSeconds, timerInterface->Name());
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -2328,6 +2328,9 @@
         .Check(request);
 
     int64_t nSleepTime;
+    int64_t relock_time;
+    // Prevent concurrent calls to walletpassphrase with the same wallet.
+    LOCK(pwallet->m_unlock_mutex);
     {
         LOCK(pwallet->cs_wallet);
 
@@ -2375,6 +2378,7 @@
         pwallet->TopUpKeyPool();
 
         pwallet->nRelockTime = GetTime() + nSleepTime;
+        relock_time = pwallet->nRelockTime;
     }
 
     // rpcRunLater must be called without cs_wallet held otherwise a deadlock
@@ -2388,9 +2392,13 @@
     std::weak_ptr<CWallet> weak_wallet = wallet;
     pwallet->chain().rpcRunLater(
         strprintf("lockwallet(%s)", pwallet->GetName()),
-        [weak_wallet] {
+        [weak_wallet, relock_time] {
             if (auto shared_wallet = weak_wallet.lock()) {
                 LOCK(shared_wallet->cs_wallet);
+                // Skip if this is not the most recent rpcRunLater callback.
+                if (shared_wallet->nRelockTime != relock_time) {
+                    return;
+                }
                 shared_wallet->Lock();
                 shared_wallet->nRelockTime = 0;
             }
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -1022,8 +1022,10 @@
     //! Holds a timestamp at which point the wallet is scheduled (externally) to
     //! be relocked. Caller must arrange for actual relocking to occur via
     //! Lock().
-    int64_t nRelockTime = 0;
+    int64_t nRelockTime GUARDED_BY(cs_wallet){0};
 
+    // Used to prevent concurrent calls to walletpassphrase RPC.
+    Mutex m_unlock_mutex;
     bool Unlock(const SecureString &strWalletPassphrase,
                 bool accept_no_keys = false);
     bool ChangeWalletPassphrase(const SecureString &strOldWalletPassphrase,