diff --git a/canopen/nmt.py b/canopen/nmt.py
index 77d56910..aca7731e 100644
--- a/canopen/nmt.py
+++ b/canopen/nmt.py
@@ -1,7 +1,6 @@
 import logging
 import struct
 import threading
-import time
 from typing import Callable, Final, Optional, TYPE_CHECKING
 
 import canopen.network
@@ -113,6 +112,7 @@ class NmtMaster(NmtBase):
     def __init__(self, node_id: int):
         super(NmtMaster, self).__init__(node_id)
         self._state_received = None
+        self._bootup_received = False
         self._node_guarding_producer: Optional[PeriodicMessageTask] = None
         #: Timestamp of last heartbeat message
         self.timestamp: Optional[float] = None
@@ -130,6 +130,7 @@ def on_heartbeat(self, can_id, data, timestamp):
             if new_state == 0:
                 # Boot-up, will go to PRE-OPERATIONAL automatically
                 self._state = 127
+                self._bootup_received = True
             else:
                 self._state = new_state
             self._state_received = new_state
@@ -160,16 +161,12 @@ def wait_for_heartbeat(self, timeout: float = 10):
 
     def wait_for_bootup(self, timeout: float = 10) -> None:
         """Wait until a boot-up message is received."""
-        end_time = time.time() + timeout
-        while True:
-            now = time.time()
-            with self.state_update:
-                self._state_received = None
-                self.state_update.wait(end_time - now + 0.1)
-            if now > end_time:
+        with self.state_update:
+            # A heartbeat can overwrite _state_received before this thread
+            # wakes up, so the boot-up is remembered in a flag of its own.
+            self._bootup_received = False
+            if not self.state_update.wait_for(lambda: self._bootup_received, timeout):
                 raise NmtError("Timeout waiting for boot-up message")
-            if self._state_received == 0:
-                break
 
     def add_heartbeat_callback(self, callback: Callable[[int], None]):
         """Add function to be called on heartbeat reception.
diff --git a/test/test_nmt.py b/test/test_nmt.py
index 7b1b7e1d..1b31313e 100644
--- a/test/test_nmt.py
+++ b/test/test_nmt.py
@@ -91,6 +91,23 @@ def test_nmt_master_wait_for_bootup(self):
         self.node.nmt.wait_for_bootup(self.TIMEOUT)
         self.assertEqual(self.node.nmt.state, "PRE-OPERATIONAL")
 
+    def test_nmt_master_wait_for_bootup_then_heartbeat(self):
+        # A heartbeat handled right after the boot-up message, before the
+        # waiting thread gets to run, must not hide the boot-up.
+        nmt = self.node.nmt
+        cob_id = 0x700 + self.NODE_ID
+
+        def boot():
+            with nmt.state_update:
+                nmt.on_heartbeat(cob_id, b"\x00", 0.0)
+                nmt.on_heartbeat(cob_id, b"\x7f", 0.0)
+
+        t = threading.Timer(0.01, boot)
+        t.start()
+        self.addCleanup(t.join)
+        nmt.wait_for_bootup(self.TIMEOUT)
+        self.assertEqual(nmt.state, "PRE-OPERATIONAL")
+
     def test_nmt_master_on_heartbeat_initialising(self):
         t = threading.Timer(0.01, self.dispatch_heartbeat, args=(0x00,))
         t.start()