diff --git a/libraries/chain/platform_timer_asio_fallback.cpp b/libraries/chain/platform_timer_asio_fallback.cpp
index 7ec808e128..b82552e412 100644
--- a/libraries/chain/platform_timer_asio_fallback.cpp
+++ b/libraries/chain/platform_timer_asio_fallback.cpp
@@ -57,36 +57,40 @@ platform_timer::~platform_timer() {
 
 void platform_timer::start(fc::time_point tp) {
    if(tp == fc::time_point::maximum()) {
-      expired = 0;
+      expired = false;
       return;
    }
    fc::microseconds x = tp.time_since_epoch() - fc::time_point::now().time_since_epoch();
    if(x.count() <= 0)
-      expired = 1;
+      expired = true;
    else {
 #if 0
       std::promise<void> p;
       auto f = p.get_future();
       checktime_ios->post([&p,this]() {
-         expired = 0;
+         expired = false;
          p.set_value();
       });
       f.get();
 #endif
-      expired = 0;
+      expired = false;
       my->timer->expires_after(std::chrono::microseconds(x.count()));
       my->timer->async_wait([this](const boost::system::error_code& ec) {
          if(ec)
             return;
-         expired = 1;
-         call_expiration_callback();
+         bool expected = false;
+         if (expired.compare_exchange_strong(expected, true)) {
+            call_expiration_callback();
+         }
       });
    }
 }
 
 void platform_timer::expire_now() {
-   expired = 1;
-   call_expiration_callback();
+   bool expected = false;
+   if (expired.compare_exchange_strong(expected, true)) {
+      call_expiration_callback();
+   }
 }
 
 void platform_timer::stop() {
@@ -94,7 +98,7 @@ void platform_timer::stop() {
       return;
 
    my->timer->cancel();
-   expired = 1;
+   expired = true;
 }
 
 }}
diff --git a/libraries/chain/platform_timer_kqueue.cpp b/libraries/chain/platform_timer_kqueue.cpp
index 3e9dc68104..823428c804 100644
--- a/libraries/chain/platform_timer_kqueue.cpp
+++ b/libraries/chain/platform_timer_kqueue.cpp
@@ -58,8 +58,10 @@ platform_timer::platform_timer() {
 
             if(c == 1 && anEvent.filter == EVFILT_TIMER) {
                platform_timer* self = (platform_timer*)anEvent.udata;
-               self->expired = 1;
-               self->call_expiration_callback();
+               bool expected = false;
+               if (self->expired.compare_exchange_strong(expected, true)) {
+                  self->call_expiration_callback();
+               }
             }
             else if(c == 1 && anEvent.filter == EVFILT_USER)
                return;
@@ -90,25 +92,27 @@ platform_timer::~platform_timer() {
 
 void platform_timer::start(fc::time_point tp) {
    if(tp == fc::time_point::maximum()) {
-      expired = 0;
+      expired = false;
       return;
    }
    fc::microseconds x = tp.time_since_epoch() - fc::time_point::now().time_since_epoch();
    if(x.count() <= 0)
-      expired = 1;
+      expired = true;
    else {
       struct kevent64_s aTimerEvent;
       EV_SET64(&aTimerEvent, my->timerid, EVFILT_TIMER, EV_ADD|EV_ENABLE|EV_ONESHOT, NOTE_USECONDS|NOTE_CRITICAL, x.count(), (uint64_t)this, 0, 0);
 
-      expired = 0;
+      expired = false;
       if(kevent64(kqueue_fd, &aTimerEvent, 1, NULL, 0, KEVENT_FLAG_IMMEDIATE, NULL) != 0)
-         expired = 1;
+         expired = true;
    }
 }
 
 void platform_timer::expire_now() {
-   expired = 1;
-   call_expiration_callback();
+   bool expected = false;
+   if (expired.compare_exchange_strong(expected, true)) {
+      call_expiration_callback();
+   }
 }
 
 void platform_timer::stop() {
@@ -118,7 +122,7 @@ void platform_timer::stop() {
    struct kevent64_s stop_timer_event;
    EV_SET64(&stop_timer_event, my->timerid, EVFILT_TIMER, EV_DELETE, 0, 0, 0, 0, 0);
    kevent64(kqueue_fd, &stop_timer_event, 1, NULL, 0, KEVENT_FLAG_IMMEDIATE, NULL);
-   expired = 1;
+   expired = true;
 }
 
 }}
diff --git a/libraries/chain/platform_timer_posix.cpp b/libraries/chain/platform_timer_posix.cpp
index 0a50ebcade..3702333c32 100644
--- a/libraries/chain/platform_timer_posix.cpp
+++ b/libraries/chain/platform_timer_posix.cpp
@@ -5,12 +5,14 @@
 #include <fc/fwd_impl.hpp>
 #include <fc/exception/exception.hpp>
 
+#include <atomic>
 #include <mutex>
 
 #include <signal.h>
 #include <time.h>
+#include <sys/types.h>
 
-namespace eosio { namespace chain {
+namespace eosio::chain {
 
 static_assert(std::atomic_bool::is_always_lock_free, "Only lock-free atomics AS-safe.");
 
@@ -19,8 +21,10 @@ struct platform_timer::impl {
 
    static void sig_handler(int, siginfo_t* si, void*) {
       platform_timer* self = (platform_timer*)si->si_value.sival_ptr;
-      self->expired = 1;
-      self->call_expiration_callback();
+      bool expected = false;
+      if (self->expired.compare_exchange_strong(expected, true)) {
+         self->call_expiration_callback();
+      }
    }
 };
 
@@ -28,9 +32,9 @@ platform_timer::platform_timer() {
    static_assert(sizeof(impl) <= fwd_size);
 
    static bool initialized;
-   static std::mutex initalized_mutex;
+   static std::mutex initialized_mutex;
 
-   if(std::lock_guard guard(initalized_mutex); !initialized) {
+   if(std::lock_guard guard(initialized_mutex); !initialized) {
       struct sigaction act;
       sigemptyset(&act.sa_mask);
       act.sa_sigaction = impl::sig_handler;
@@ -55,25 +59,27 @@ platform_timer::~platform_timer() {
 
 void platform_timer::start(fc::time_point tp) {
    if(tp == fc::time_point::maximum()) {
-      expired = 0;
+      expired = false;
       return;
    }
    fc::microseconds x = tp.time_since_epoch() - fc::time_point::now().time_since_epoch();
    if(x.count() <= 0)
-      expired = 1;
+      expired = true;
    else {
       time_t secs = x.count() / 1000000;
       long nsec = (x.count() - (secs*1000000)) * 1000;
       struct itimerspec enable = {{0, 0}, {secs, nsec}};
-      expired = 0;
+      expired = false;
       if(timer_settime(my->timerid, 0, &enable, NULL) != 0)
-         expired = 1;
+         expired = true;
    }
 }
 
 void platform_timer::expire_now() {
-   expired = 1;
-   call_expiration_callback();
+   bool expected = false;
+   if (expired.compare_exchange_strong(expected, true)) {
+      call_expiration_callback();
+   }
 }
 
 void platform_timer::stop() {
@@ -81,7 +87,7 @@ void platform_timer::stop() {
       return;
    struct itimerspec disable = {{0, 0}, {0, 0}};
    timer_settime(my->timerid, 0, &disable, NULL);
-   expired = 1;
+   expired = true;
 }
 
-}}
+}