diff --git a/asyncpg/protocol/protocol.pxd b/asyncpg/protocol/protocol.pxd
index 5f144e55..a9ac8d5f 100644
--- a/asyncpg/protocol/protocol.pxd
+++ b/asyncpg/protocol/protocol.pxd
@@ -39,8 +39,6 @@ cdef class BaseProtocol(CoreProtocol):
         bint return_extra
         object create_future
         object timeout_handle
-        object timeout_callback
-        object completed_callback
         object conref
         type record_class
         bint is_reading
diff --git a/asyncpg/protocol/protocol.pyx b/asyncpg/protocol/protocol.pyx
index 1f739cc2..487259eb 100644
--- a/asyncpg/protocol/protocol.pyx
+++ b/asyncpg/protocol/protocol.pyx
@@ -98,8 +98,6 @@ cdef class BaseProtocol(CoreProtocol):
         self.writing_allowed.set()
 
         self.timeout_handle = None
-        self.timeout_callback = self._on_timeout
-        self.completed_callback = self._on_waiter_completed
 
         self.queries_count = 0
 
@@ -584,6 +582,7 @@ cdef class BaseProtocol(CoreProtocol):
         self._handle_waiter_on_connection_lost(None)
         self._terminate()
         self.transport.abort()
+        self.transport = None
 
     @cython.iterable_coroutine
     async def close(self, timeout):
@@ -754,8 +753,8 @@ cdef class BaseProtocol(CoreProtocol):
         self.waiter = self.create_future()
         if timeout is not None:
             self.timeout_handle = self.loop.call_later(
-                timeout, self.timeout_callback, self.waiter)
-        self.waiter.add_done_callback(self.completed_callback)
+                timeout, self._on_timeout, self.waiter)
+        self.waiter.add_done_callback(self._on_waiter_completed)
         return self.waiter
 
     cdef _on_result__connect(self, object waiter):
diff --git a/tests/test_connect.py b/tests/test_connect.py
index f61db61a..1af074f1 100644
--- a/tests/test_connect.py
+++ b/tests/test_connect.py
@@ -7,6 +7,7 @@
 
 import asyncio
 import contextlib
+import gc
 import ipaddress
 import os
 import pathlib
@@ -1846,14 +1847,27 @@ async def worker():
 class TestConnectionGC(tb.ClusterTestCase):
 
     async def _run_no_explicit_close_test(self):
-        con = await self.connect()
-        await con.fetchval("select 123")
-        proto = con._protocol
-        conref = weakref.ref(con)
-        del con
-
-        self.assertIsNone(conref())
-        self.assertTrue(proto.is_closed())
+        gc_was_enabled = gc.isenabled()
+        gc.disable()
+        try:
+            con = await self.connect()
+            await con.fetchval("select 123")
+            proto = con._protocol
+            conref = weakref.ref(con)
+            del con
+
+            self.assertIsNone(conref())
+            self.assertTrue(proto.is_closed())
+
+            # tick event loop; asyncio.selector_events._SelectorSocketTransport
+            # needs a chance to close itself and remove its reference to proto
+            await asyncio.sleep(0)
+            protoref = weakref.ref(proto)
+            del proto
+            self.assertIsNone(protoref())
+        finally:
+            if gc_was_enabled:
+                gc.enable()
 
     async def test_no_explicit_close_no_debug(self):
         olddebug = self.loop.get_debug()