diff --git a/hydra/doctor.py b/hydra/doctor.py
index 29eb37a..dd1c5d1 100644
--- a/hydra/doctor.py
+++ b/hydra/doctor.py
@@ -138,9 +138,11 @@ def doctor_report(*, proc_root=Path('/proc'), sys_root=Path('/sys'), dev_root=Pa
     inputs = [p for p in _entries(sys_root / 'class/input') if re.fullmatch(r'event[0-9]+', p.name)]
     keyboards = 0
     for path in inputs:
-        value = _read(path / 'device/capabilities/key', 256).strip().replace(' ', '')
-        if re.fullmatch(r'[0-9a-fA-F]{1,256}', value):
-            bits = int(value, 16)
+        words = _read(path / 'device/capabilities/key', 256).split()
+        if words and all(re.fullmatch(r'[0-9a-fA-F]{1,16}', word) for word in words):
+            # x86_64 sysfs prints most-significant unsigned-long words first,
+            # without zero padding. KEY_A (30) and KEY_Z (44) are in the low word.
+            bits = int(words[-1], 16)
             keyboards += bool(bits & (1 << 30) and bits & (1 << 44))
     return {
         'format': 1,
diff --git a/tests/test_doctor.py b/tests/test_doctor.py
index 6f8e4d1..158598b 100644
--- a/tests/test_doctor.py
+++ b/tests/test_doctor.py
@@ -78,6 +78,16 @@ class DoctorTests(unittest.TestCase):
         for secret in ('PRIVATE_SERIAL', 'PRIVATE_USER', 'PRIVATE_SSID', 'aa:bb:cc:dd:ee:ff'):
             self.assertNotIn(secret, encoded)
 
+    def test_keyboard_detection_preserves_64_bit_capability_word_boundaries(self):
+        capability = self.file('sys/class/input/event0/device/capabilities/key')
+        for bitmap, expected in (('10004000000 0\n', 0),
+                                 ('1 100040000000\n', 1),
+                                 ('100040000000\n', 1),
+                                 ('10004000000 invalid\n', 0)):
+            with self.subTest(bitmap=bitmap):
+                capability.write_text(bitmap)
+                self.assertEqual(self.report()['input']['keyboards'], expected)
+
     def test_probes_timeout_independently_and_discard_untrusted_output(self):
         calls = []
         def run(command, **kwargs):