diff --git a/bin/common_trans.cc b/bin/common_trans.cc
index e3df2316b..9c1f27a15 100644
--- a/bin/common_trans.cc
+++ b/bin/common_trans.cc
@@ -1,5 +1,5 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2015-2019 Laboratoire de Recherche et Développement
+// Copyright (C) 2015-2020 Laboratoire de Recherche et Développement
 // de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
@@ -457,12 +457,12 @@ autproc_runner::round_automaton(spot::const_twa_graph_ptr aut, unsigned serial)
   filename_automaton.new_round(aut, serial);
 }
 
-volatile bool timed_out = false;
+std::atomic<bool> timed_out{false};
 unsigned timeout_count = 0;
 
 static unsigned timeout = 0;
 #if ENABLE_TIMEOUT
-static volatile int alarm_on = 0;
+static std::atomic<int> alarm_on{0};
 static int child_pid = -1;
 
 static void
diff --git a/bin/common_trans.hh b/bin/common_trans.hh
index d95350abc..e01131350 100644
--- a/bin/common_trans.hh
+++ b/bin/common_trans.hh
@@ -1,6 +1,6 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2015-2018 Laboratoire de Recherche et Développement
-// de l'Epita (LRDE).
+// Copyright (C) 2015-2018, 2020 Laboratoire de Recherche et
+// Développement de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -21,6 +21,7 @@
 
 #include "common_sys.hh"
 #include <vector>
+#include <atomic>
 #include <argp.h>
 
 #include <spot/misc/formater.hh>
@@ -165,7 +166,7 @@ public:
 # define ENABLE_TIMEOUT 0
 #endif
 
-extern volatile bool timed_out;
+extern std::atomic<bool> timed_out;
 extern unsigned timeout_count;
 #if ENABLE_TIMEOUT
 void setup_sig_handler();
diff --git a/spot/tl/formula.hh b/spot/tl/formula.hh
index 8b1340aaa..57cc8f91c 100644
--- a/spot/tl/formula.hh
+++ b/spot/tl/formula.hh
@@ -842,7 +842,7 @@ namespace spot
       return ptr_ != nullptr;
     }
 
-    operator bool() const
+    operator bool() const noexcept
     {
       return ptr_ != nullptr;
     }