diff --git a/asyncpg/protocol/coreproto.pyx b/asyncpg/protocol/coreproto.pyx
index da96c412..5470d6fa 100644
--- a/asyncpg/protocol/coreproto.pyx
+++ b/asyncpg/protocol/coreproto.pyx
@@ -573,8 +573,14 @@ cdef class CoreProtocol:
 
         elif status == AUTH_REQUIRED_PASSWORD:
             # AuthenticationCleartextPassword
-            self.result_type = RESULT_OK
-            self.auth_msg = self._auth_password_message_cleartext()
+            if self.password is None:
+                self.result_type = RESULT_FAILED
+                self.result = apg_exc.InterfaceError(
+                    'password authentication requested by server, '
+                    'but no password was supplied')
+            else:
+                self.result_type = RESULT_OK
+                self.auth_msg = self._auth_password_message_cleartext()
 
         elif status == AUTH_REQUIRED_PASSWORDMD5:
             # AuthenticationMD5Password
diff --git a/tests/test_connect.py b/tests/test_connect.py
index 955fb825..ba6ac0ea 100644
--- a/tests/test_connect.py
+++ b/tests/test_connect.py
@@ -266,6 +266,12 @@ async def test_auth_password_cleartext(self):
                 user='password_user',
                 password='wrongpassword')
 
+    async def test_auth_password_cleartext_without_password(self):
+        with self.assertRaisesRegex(
+                asyncpg.InterfaceError, 'no password was supplied'):
+            await self._try_connect(
+                user='password_user', password=None)
+
     async def test_auth_password_cleartext_callable(self):
         def get_correctpassword():
             return CORRECT_PASSWORD