diff --git a/trio/_highlevel_open_unix_stream.py b/trio/_highlevel_open_unix_stream.py
index 5992c4f73e..59141ebc38 100644
--- a/trio/_highlevel_open_unix_stream.py
+++ b/trio/_highlevel_open_unix_stream.py
@@ -40,13 +40,10 @@ async def open_unix_socket(filename,):
     if not has_unix:
         raise RuntimeError("Unix sockets are not supported on this platform")
 
-    if filename is None:
-        raise ValueError("Filename cannot be None")
-
     # much more simplified logic vs tcp sockets - one socket type and only one
     # possible location to connect to
     sock = socket(AF_UNIX, SOCK_STREAM)
     with close_on_error(sock):
-        await sock.connect(filename)
+        await sock.connect(trio._util.fspath(filename))
 
     return trio.SocketStream(sock)
diff --git a/trio/tests/test_highlevel_open_unix_stream.py b/trio/tests/test_highlevel_open_unix_stream.py
index c66028b14f..872a43dd6d 100644
--- a/trio/tests/test_highlevel_open_unix_stream.py
+++ b/trio/tests/test_highlevel_open_unix_stream.py
@@ -30,6 +30,12 @@ def close(self):
     assert c.closed
 
 
+@pytest.mark.parametrize('filename', [4, 4.5])
+async def test_open_with_bad_filename_type(filename):
+    with pytest.raises(TypeError):
+        await open_unix_socket(filename)
+
+
 async def test_open_bad_socket():
     # mktemp is marked as insecure, but that's okay, we don't want the file to
     # exist