diff --git a/kformat/kproperty.py b/kformat/kproperty.py
index 9ac915c..dda9d1e 100644
--- a/kformat/kproperty.py
+++ b/kformat/kproperty.py
@@ -44,9 +44,17 @@ def __init__(
         )
 
     def to_bytes(self, v: Optional) -> bytes:
-        s = str(int(v)) if v is not None else ''
         try:
-            b = bytes(s, encoding=N.ENCODING).rjust(self.length, self.filler)
+            p = b'-' if v < 0 else b''
+            s = str(int(abs(v)))
+        except TypeError:
+            p, s = b'', ''
+
+        try:
+            b = p + bytes(s, encoding=N.ENCODING).rjust(
+                self.length - len(p),
+                self.filler
+            )
             assert len(b) <= self.length
             return b
         except AssertionError:
diff --git a/tests/test_kclass.py b/tests/test_kclass.py
index 15bd64f..42c74ce 100644
--- a/tests/test_kclass.py
+++ b/tests/test_kclass.py
@@ -25,7 +25,7 @@ class Something:
         sth = Something(
             123,
             'k-class',
-            Other(456, 'subclass'),
+            Other(-456, 'subclass'),
             [],
             None
         )
diff --git a/tests/test_kproperty.py b/tests/test_kproperty.py
index 2114643..e4fdbbb 100644
--- a/tests/test_kproperty.py
+++ b/tests/test_kproperty.py
@@ -23,14 +23,29 @@ def test_N_to_bytes(self):
             N(5).to_bytes(12345),
             b'12345'
         )
+        self.assertEqual(
+            N(5).to_bytes(-1),
+            b'-0001'
+        )
+        self.assertEqual(
+            N(3).to_bytes(-12),
+            b'-12'
+        )
         self.assertEqual(
             N(10, filler=b'?').to_bytes(3),
             b'?????????3'
         )
+        self.assertEqual(
+            N(5, filler=b'-').to_bytes(3),
+            b'----3'
+        )
 
         with self.assertRaises(ValueError):
             N(3).to_bytes(1234)
 
+        with self.assertRaises(ValueError):
+            N(2).to_bytes(-10)
+
     def test_AN_to_bytes(self):
         self.assertEqual(
             AN(10).to_bytes('sunghyunzz'),