diff --git a/asyncpg/connection.py b/asyncpg/connection.py
index 4b4d8a23..b7266471 100644
--- a/asyncpg/connection.py
+++ b/asyncpg/connection.py
@@ -342,13 +342,16 @@ async def _get_statement(
         *,
         named: bool=False,
         use_cache: bool=True,
+        ignore_custom_codec=False,
         record_class=None
     ):
         if record_class is None:
             record_class = self._protocol.get_record_class()
 
         if use_cache:
-            statement = self._stmt_cache.get((query, record_class))
+            statement = self._stmt_cache.get(
+                (query, record_class, ignore_custom_codec)
+            )
             if statement is not None:
                 return statement
 
@@ -371,6 +374,7 @@ async def _get_statement(
             query,
             timeout,
             record_class=record_class,
+            ignore_custom_codec=ignore_custom_codec,
         )
         need_reprepare = False
         types_with_missing_codecs = statement._init_types()
@@ -415,7 +419,8 @@ async def _get_statement(
             )
 
         if use_cache:
-            self._stmt_cache.put((query, record_class), statement)
+            self._stmt_cache.put(
+                (query, record_class, ignore_custom_codec), statement)
 
         # If we've just created a new statement object, check if there
         # are any statements for GC.
@@ -426,7 +431,12 @@ async def _get_statement(
 
     async def _introspect_types(self, typeoids, timeout):
         return await self.__execute(
-            self._intro_query, (list(typeoids),), 0, timeout)
+            self._intro_query,
+            (list(typeoids),),
+            0,
+            timeout,
+            ignore_custom_codec=True,
+        )
 
     async def _introspect_type(self, typename, schema):
         if (
@@ -439,20 +449,22 @@ async def _introspect_type(self, typename, schema):
                 [typeoid],
                 limit=0,
                 timeout=None,
+                ignore_custom_codec=True,
             )
-            if rows:
-                typeinfo = rows[0]
-            else:
-                typeinfo = None
         else:
-            typeinfo = await self.fetchrow(
-                introspection.TYPE_BY_NAME, typename, schema)
+            rows = await self._execute(
+                introspection.TYPE_BY_NAME,
+                [typename, schema],
+                limit=1,
+                timeout=None,
+                ignore_custom_codec=True,
+            )
 
-        if not typeinfo:
+        if not rows:
             raise ValueError(
                 'unknown type: {}.{}'.format(schema, typename))
 
-        return typeinfo
+        return rows[0]
 
     def cursor(
         self,
@@ -1325,7 +1337,9 @@ def _mark_stmts_as_closed(self):
     def _maybe_gc_stmt(self, stmt):
         if (
             stmt.refs == 0
-            and not self._stmt_cache.has((stmt.query, stmt.record_class))
+            and not self._stmt_cache.has(
+                (stmt.query, stmt.record_class, stmt.ignore_custom_codec)
+            )
         ):
             # If low-level `stmt` isn't referenced from any high-level
             # `PreparedStatement` object and is not in the `_stmt_cache`:
@@ -1589,6 +1603,7 @@ async def _execute(
         timeout,
         *,
         return_status=False,
+        ignore_custom_codec=False,
         record_class=None
     ):
         with self._stmt_exclusive_section:
@@ -1599,6 +1614,7 @@ async def _execute(
                 timeout,
                 return_status=return_status,
                 record_class=record_class,
+                ignore_custom_codec=ignore_custom_codec,
             )
         return result
 
@@ -1610,6 +1626,7 @@ async def __execute(
         timeout,
         *,
         return_status=False,
+        ignore_custom_codec=False,
         record_class=None
     ):
         executor = lambda stmt, timeout: self._protocol.bind_execute(
@@ -1620,6 +1637,7 @@ async def __execute(
             executor,
             timeout,
             record_class=record_class,
+            ignore_custom_codec=ignore_custom_codec,
         )
 
     async def _executemany(self, query, args, timeout):
@@ -1637,6 +1655,7 @@ async def _do_execute(
         timeout,
         retry=True,
         *,
+        ignore_custom_codec=False,
         record_class=None
     ):
         if timeout is None:
@@ -1644,6 +1663,7 @@ async def _do_execute(
                 query,
                 None,
                 record_class=record_class,
+                ignore_custom_codec=ignore_custom_codec,
             )
         else:
             before = time.monotonic()
@@ -1651,6 +1671,7 @@ async def _do_execute(
                 query,
                 timeout,
                 record_class=record_class,
+                ignore_custom_codec=ignore_custom_codec,
             )
             after = time.monotonic()
             timeout -= after - before
diff --git a/asyncpg/protocol/codecs/base.pxd b/asyncpg/protocol/codecs/base.pxd
index be1f0a3f..e8136f7b 100644
--- a/asyncpg/protocol/codecs/base.pxd
+++ b/asyncpg/protocol/codecs/base.pxd
@@ -166,5 +166,6 @@ cdef class DataCodecConfig:
         dict _derived_type_codecs
         dict _custom_type_codecs
 
-    cdef inline Codec get_codec(self, uint32_t oid, ServerDataFormat format)
+    cdef inline Codec get_codec(self, uint32_t oid, ServerDataFormat format,
+                                bint ignore_custom_codec=*)
     cdef inline Codec get_any_local_codec(self, uint32_t oid)
diff --git a/asyncpg/protocol/codecs/base.pyx b/asyncpg/protocol/codecs/base.pyx
index 238fa280..1c930cd0 100644
--- a/asyncpg/protocol/codecs/base.pyx
+++ b/asyncpg/protocol/codecs/base.pyx
@@ -692,18 +692,20 @@ cdef class DataCodecConfig:
 
         return codec
 
-    cdef inline Codec get_codec(self, uint32_t oid, ServerDataFormat format):
+    cdef inline Codec get_codec(self, uint32_t oid, ServerDataFormat format,
+                                bint ignore_custom_codec=False):
         cdef Codec codec
 
-        codec = self.get_any_local_codec(oid)
-        if codec is not None:
-            if codec.format != format:
-                # The codec for this OID has been overridden by
-                # set_{builtin}_type_codec with a different format.
-                # We must respect that and not return a core codec.
-                return None
-            else:
-                return codec
+        if not ignore_custom_codec:
+            codec = self.get_any_local_codec(oid)
+            if codec is not None:
+                if codec.format != format:
+                    # The codec for this OID has been overridden by
+                    # set_{builtin}_type_codec with a different format.
+                    # We must respect that and not return a core codec.
+                    return None
+                else:
+                    return codec
 
         codec = get_core_codec(oid, format)
         if codec is not None:
diff --git a/asyncpg/protocol/prepared_stmt.pxd b/asyncpg/protocol/prepared_stmt.pxd
index 90944c1a..4427bfdc 100644
--- a/asyncpg/protocol/prepared_stmt.pxd
+++ b/asyncpg/protocol/prepared_stmt.pxd
@@ -12,6 +12,7 @@ cdef class PreparedStatementState:
         readonly bint closed
         readonly int refs
         readonly type record_class
+        readonly bint ignore_custom_codec
 
 
         list         row_desc
diff --git a/asyncpg/protocol/prepared_stmt.pyx b/asyncpg/protocol/prepared_stmt.pyx
index 60094be6..fd9f5a26 100644
--- a/asyncpg/protocol/prepared_stmt.pyx
+++ b/asyncpg/protocol/prepared_stmt.pyx
@@ -16,7 +16,8 @@ cdef class PreparedStatementState:
         str name,
         str query,
         BaseProtocol protocol,
-        type record_class
+        type record_class,
+        bint ignore_custom_codec
     ):
         self.name = name
         self.query = query
@@ -28,6 +29,7 @@ cdef class PreparedStatementState:
         self.closed = False
         self.refs = 0
         self.record_class = record_class
+        self.ignore_custom_codec = ignore_custom_codec
 
     def _get_parameters(self):
         cdef Codec codec
@@ -205,7 +207,8 @@ cdef class PreparedStatementState:
             cols_mapping[col_name] = i
             cols_names.append(col_name)
             oid = row[3]
-            codec = self.settings.get_data_codec(oid)
+            codec = self.settings.get_data_codec(
+                oid, ignore_custom_codec=self.ignore_custom_codec)
             if codec is None or not codec.has_decoder():
                 raise exceptions.InternalClientError(
                     'no decoder for OID {}'.format(oid))
@@ -230,7 +233,8 @@ cdef class PreparedStatementState:
 
         for i from 0 <= i < self.args_num:
             p_oid = self.parameters_desc[i]
-            codec = self.settings.get_data_codec(p_oid)
+            codec = self.settings.get_data_codec(
+                p_oid, ignore_custom_codec=self.ignore_custom_codec)
             if codec is None or not codec.has_encoder():
                 raise exceptions.InternalClientError(
                     'no encoder for OID {}'.format(p_oid))
diff --git a/asyncpg/protocol/protocol.pyx b/asyncpg/protocol/protocol.pyx
index 4f7ce675..a6d9ad5d 100644
--- a/asyncpg/protocol/protocol.pyx
+++ b/asyncpg/protocol/protocol.pyx
@@ -145,6 +145,7 @@ cdef class BaseProtocol(CoreProtocol):
     async def prepare(self, stmt_name, query, timeout,
                       *,
                       PreparedStatementState state=None,
+                      ignore_custom_codec=False,
                       record_class):
         if self.cancel_waiter is not None:
             await self.cancel_waiter
@@ -161,7 +162,7 @@ cdef class BaseProtocol(CoreProtocol):
             self.last_query = query
             if state is None:
                 state = PreparedStatementState(
-                    stmt_name, query, self, record_class)
+                    stmt_name, query, self, record_class, ignore_custom_codec)
             self.statement = state
         except Exception as ex:
             waiter.set_exception(ex)
diff --git a/asyncpg/protocol/settings.pxd b/asyncpg/protocol/settings.pxd
index 44b673c2..41131cdc 100644
--- a/asyncpg/protocol/settings.pxd
+++ b/asyncpg/protocol/settings.pxd
@@ -26,4 +26,5 @@ cdef class ConnectionSettings(pgproto.CodecContext):
     cpdef inline set_builtin_type_codec(
         self, typeoid, typename, typeschema, typekind, alias_to, format)
     cpdef inline Codec get_data_codec(
-        self, uint32_t oid, ServerDataFormat format=*)
+        self, uint32_t oid, ServerDataFormat format=*,
+        bint ignore_custom_codec=*)
diff --git a/asyncpg/protocol/settings.pyx b/asyncpg/protocol/settings.pyx
index 2ea72169..6121fce4 100644
--- a/asyncpg/protocol/settings.pyx
+++ b/asyncpg/protocol/settings.pyx
@@ -87,14 +87,18 @@ cdef class ConnectionSettings(pgproto.CodecContext):
                                                  typekind, alias_to, _format)
 
     cpdef inline Codec get_data_codec(self, uint32_t oid,
-                                      ServerDataFormat format=PG_FORMAT_ANY):
+                                      ServerDataFormat format=PG_FORMAT_ANY,
+                                      bint ignore_custom_codec=False):
         if format == PG_FORMAT_ANY:
-            codec = self._data_codecs.get_codec(oid, PG_FORMAT_BINARY)
+            codec = self._data_codecs.get_codec(
+                oid, PG_FORMAT_BINARY, ignore_custom_codec)
             if codec is None:
-                codec = self._data_codecs.get_codec(oid, PG_FORMAT_TEXT)
+                codec = self._data_codecs.get_codec(
+                    oid, PG_FORMAT_TEXT, ignore_custom_codec)
             return codec
         else:
-            return self._data_codecs.get_codec(oid, format)
+            return self._data_codecs.get_codec(
+                oid, format, ignore_custom_codec)
 
     def __getattr__(self, name):
         if not name.startswith('_'):
diff --git a/tests/test_introspection.py b/tests/test_introspection.py
index eb3258f9..7de4236f 100644
--- a/tests/test_introspection.py
+++ b/tests/test_introspection.py
@@ -43,6 +43,20 @@ def tearDownClass(cls):
 
         super().tearDownClass()
 
+    def setUp(self):
+        super().setUp()
+        self.loop.run_until_complete(self._add_custom_codec(self.con))
+
+    async def _add_custom_codec(self, conn):
+        # mess up with the codec - builtin introspection shouldn't be affected
+        await conn.set_type_codec(
+            "oid",
+            schema="pg_catalog",
+            encoder=lambda value: None,
+            decoder=lambda value: None,
+            format="text",
+        )
+
     @tb.with_connection_options(database='asyncpg_intro_test')
     async def test_introspection_on_large_db(self):
         await self.con.execute(
@@ -142,6 +156,7 @@ async def test_introspection_retries_after_cache_bust(self):
         # query would cause introspection to retry.
         slow_intro_conn = await self.connect(
             connection_class=SlowIntrospectionConnection)
+        await self._add_custom_codec(slow_intro_conn)
         try:
             await self.con.execute('''
                 CREATE DOMAIN intro_1_t AS int;