diff --git a/pslab/bus/busio.py b/pslab/bus/busio.py
index 97771dc..5de6074 100644
--- a/pslab/bus/busio.py
+++ b/pslab/bus/busio.py
@@ -90,7 +90,7 @@ def scan(self) -> List[int]:
         addrs : list of int
             List of 7-bit addresses on which slave devices replied.
         """
-        return self._scan(0x08, 0x77)
+        return self._scan(0x08, 0x78)
 
     def try_lock(self) -> bool:  # pylint: disable=no-self-use
         """Just a dummy method."""
diff --git a/tests/test_busio_i2c_scan.py b/tests/test_busio_i2c_scan.py
new file mode 100644
index 0000000..eca150a
--- /dev/null
+++ b/tests/test_busio_i2c_scan.py
@@ -0,0 +1,64 @@
+"""CircuitPython-compatible scans include both permitted address endpoints."""
+
+import pytest
+
+import pslab.protocol as CP
+from pslab.bus.busio import I2C
+from pslab.connection import ConnectionHandler
+
+
+class ScanningConnection(ConnectionHandler):
+    """Interpret scan commands and return address-dependent firmware ACKs."""
+
+    def __init__(self, responding_addresses):
+        self.responding_addresses = responding_addresses
+        self.pending = bytearray()
+        self.probed = []
+        self.stopped = []
+        self.active = None
+
+    def connect(self):
+        """No physical connection is needed."""
+
+    def disconnect(self):
+        """No physical connection is needed."""
+
+    def write(self, data):
+        """Accumulate one firmware command."""
+        self.pending.extend(data)
+        return len(data)
+
+    def read(self, numbytes):
+        """Return the transport ACK with its I2C address response bit."""
+        assert numbytes == 1
+        assert self.pending[:1] == CP.I2C_HEADER
+        command = bytes(self.pending[1:2])
+        ack = 1
+        if command == CP.I2C_START:
+            assert self.active is None
+            assert self.pending[2] & 1 == 0
+            self.active = self.pending[2] >> 1
+            self.probed.append(self.active)
+            if self.active not in self.responding_addresses:
+                ack |= 0x10
+        elif command == CP.I2C_STOP:
+            assert self.active is not None
+            self.stopped.append(self.active)
+            self.active = None
+        else:
+            assert command in (CP.I2C_INIT, CP.I2C_CONFIG)
+        self.pending.clear()
+        return bytes([ack])
+
+
+@pytest.mark.parametrize(
+    "responders", [{0x77}, {0x08}, {0x08, 0x76, 0x77}, set(), {0x07, 0x78}]
+)
+def test_scan_finds_devices_through_last_nonreserved_address(responders):
+    wire = ScanningConnection(responders)
+    bus = I2C(wire)
+    assert bus.scan() == sorted(responders & set(range(0x08, 0x78)))
+    assert wire.probed == list(range(0x08, 0x78))
+    assert wire.stopped == wire.probed
+    assert wire.active is None
+    assert wire.pending == b""