diff --git a/blender_asset_tracer/bpathlib.py b/blender_asset_tracer/bpathlib.py
index 30be080..3d8c53d 100644
--- a/blender_asset_tracer/bpathlib.py
+++ b/blender_asset_tracer/bpathlib.py
@@ -15,10 +15,10 @@ class BlendPath(bytes):
 
     def __new__(cls, path):
         if isinstance(path, pathlib.Path):
-            path = str(path)  # handle as string, which is encoded to bytes below.
-        if isinstance(path, str):
-            # As a convenience, when a string is given, interpret as UTF-8.
-            return bytes.__new__(cls, path.encode('utf-8'))
+            path = str(path).encode('utf-8')
+        if not isinstance(path, bytes):
+            raise TypeError('path must be bytes or pathlib.Path, but is %r' % path)
+
         return bytes.__new__(cls, path)
 
     @classmethod
diff --git a/tests/test_bpathlib.py b/tests/test_bpathlib.py
index b6fcb4f..4f2b1ad 100644
--- a/tests/test_bpathlib.py
+++ b/tests/test_bpathlib.py
@@ -6,18 +6,13 @@ from blender_asset_tracer.bpathlib import BlendPath
 
 class BlendPathTest(unittest.TestCase):
     def test_string_path(self):
-        p = BlendPath('//some/file.blend')
+        p = BlendPath(Path('//some/file.blend'))
         self.assertEqual(b'//some/file.blend', p)
 
-        p = BlendPath(r'C:\some\file.blend')
+        p = BlendPath(Path(r'C:\some\file.blend'))
         self.assertEqual(b'C:\\some\\file.blend', p)
 
     def test_is_absolute(self):
-        self.assertFalse(BlendPath('//some/file.blend').is_absolute())
-        self.assertTrue(BlendPath('/some/file.blend').is_absolute())
-        self.assertTrue(BlendPath('C:/some/file.blend').is_absolute())
-        self.assertFalse(BlendPath('some/file.blend').is_absolute())
-
         self.assertFalse(BlendPath(b'//some/file.blend').is_absolute())
         self.assertTrue(BlendPath(b'/some/file.blend').is_absolute())
         self.assertTrue(BlendPath(b'C:/some/file.blend').is_absolute())
@@ -25,11 +20,6 @@ class BlendPathTest(unittest.TestCase):
         self.assertFalse(BlendPath(b'some/file.blend').is_absolute())
 
     def test_is_blendfile_relative(self):
-        self.assertTrue(BlendPath('//some/file.blend').is_blendfile_relative())
-        self.assertFalse(BlendPath('/some/file.blend').is_blendfile_relative())
-        self.assertFalse(BlendPath('C:/some/file.blend').is_blendfile_relative())
-        self.assertFalse(BlendPath('some/file.blend').is_blendfile_relative())
-
         self.assertTrue(BlendPath(b'//some/file.blend').is_blendfile_relative())
         self.assertFalse(BlendPath(b'/some/file.blend').is_blendfile_relative())
         self.assertFalse(BlendPath(b'C:/some/file.blend').is_blendfile_relative())