diff --git a/scapy/automaton.py b/scapy/automaton.py
index f26370b102f..f29e4d7857d 100644
--- a/scapy/automaton.py
+++ b/scapy/automaton.py
@@ -11,6 +11,7 @@
     - add documentation for ioevent, as_supersocket...
 """
 
+import copy
 import ctypes
 import itertools
 import logging
@@ -1308,6 +1309,23 @@ def _do_control(self, ready, *args, **kargs):
             k.update(kargs)
             self.parse_args(*a, **k)
 
+            # The timers are registered on the class by the @ATMT.timeout and
+            # @ATMT.timer decorators, but their runtime state (_time, _expired,
+            # _just_expired) is per-run bookkeeping. Left shared on the class,
+            # concurrently running instances of the same automaton (Automaton.spawn,
+            # ioevents used as supersockets) race for the one-shot expiry flags:
+            # whichever control thread decrements a timer first consumes the
+            # expiration, and the other instances never observe the timeout and
+            # block forever in select(). Copy the timers per started instance,
+            # after parse_args() so pre-start reconfiguration through
+            # timer_by_name() (which mutates the class-level timers) is honored.
+            self.timeout = {}  # type: Dict[str, _TimerList]
+            for state_name, timers in type(self).timeout.items():
+                timer_list = _TimerList()
+                for t in timers:
+                    timer_list.add_timer(copy.copy(t))
+                self.timeout[state_name] = timer_list
+
             # Start the automaton
             self.state = self.initial_states[0](self)
             self.send_sock = self.sock or self.send_sock_class(**self.socket_kargs)
diff --git a/test/scapy/automaton.uts b/test/scapy/automaton.uts
index 6aec9b0bbac..d71c2820de3 100644
--- a/test/scapy/automaton.uts
+++ b/test/scapy/automaton.uts
@@ -386,6 +386,42 @@ assert sm.timer_by_name("goto_end")._timeout == 1
 assert sm.count1 == 10
 assert sm.count2 == 6
 
+~ timers are per-instance when several instances run concurrently
+
+import time
+
+
+class TimerRaceTest(Automaton):
+    @ATMT.state(initial=1)
+    def BEGIN(self):
+        self.fired = False
+
+    @ATMT.timeout(BEGIN, 0.2)
+    def goto_end(self):
+        self.fired = True
+        raise self.END()
+
+    @ATMT.state(final=1)
+    def END(self):
+        pass
+
+
+a = TimerRaceTest(ll=lambda: None, recvsock=lambda: None)
+b = TimerRaceTest(ll=lambda: None, recvsock=lambda: None)
+assert a.timer_by_name("goto_end") is not None
+assert b.timer_by_name("goto_end") is not None
+
+a.runbg()
+b.runbg()
+deadline = time.time() + 10
+while time.time() < deadline and (a.isrunning() or b.isrunning()):
+    time.sleep(0.05)
+assert not a.isrunning(), "instance a never observed its timeout"
+assert not b.isrunning(), "instance b never observed its timeout"
+assert a.fired and b.fired
+a.stop()
+b.stop()
+
 ~ reconfigure timers
 
 sm = TimerTest(ll=lambda: None, recvsock=lambda: None)