diff --git a/asyncpg/protocol/coreproto.pyx b/asyncpg/protocol/coreproto.pyx
index 8e34014e..d5936c7a 100644
--- a/asyncpg/protocol/coreproto.pyx
+++ b/asyncpg/protocol/coreproto.pyx
@@ -675,7 +675,7 @@ cdef class CoreProtocol:
             WriteBuffer msg
 
         msg = WriteBuffer.new_message(b'p')
-        msg.write_bytestring(self.password.encode(self.encoding))
+        msg.write_bytestring((self.password or '').encode(self.encoding))
         msg.end_message()
 
         return msg
diff --git a/tests/test_connect.py b/tests/test_connect.py
index 839c3dcf..e00c7b6c 100644
--- a/tests/test_connect.py
+++ b/tests/test_connect.py
@@ -270,6 +270,11 @@ async def test_auth_password_cleartext(self):
                 user='password_user',
                 password='wrongpassword')
 
+    async def test_auth_password_cleartext_without_password(self):
+        with self.assertRaises(asyncpg.InvalidPasswordError):
+            await self._try_connect(
+                user='password_user', password=lambda: None)
+
     async def test_auth_password_cleartext_callable(self):
         def get_correctpassword():
             return CORRECT_PASSWORD