diff --git a/asyncpg/cursor.py b/asyncpg/cursor.py
index b4abeed1..467eaa2c 100644
--- a/asyncpg/cursor.py
+++ b/asyncpg/cursor.py
@@ -111,7 +111,7 @@ def _check_ready(self):
             raise exceptions.InterfaceError(
                 'cursor: the prepared statement is closed')
 
-        if not self._connection._top_xact:
+        if not self._connection.is_in_transaction():
             raise exceptions.NoActiveSQLTransactionError(
                 'cursor cannot be created outside of a transaction')
 
diff --git a/tests/test_cursor.py b/tests/test_cursor.py
index ad446bc3..0d625560 100644
--- a/tests/test_cursor.py
+++ b/tests/test_cursor.py
@@ -109,6 +109,17 @@ async def test_cursor_01(self):
                                     'cursor cannot be created.*transaction'):
             await st.cursor()
 
+    async def test_cursor_external_transaction(self):
+        await self.con.execute('BEGIN')
+        try:
+            st = await self.con.prepare('SELECT generate_series(0, 2)')
+            cur = await st.cursor()
+            self.assertEqual(
+                await cur.fetch(10),
+                [(0,), (1,), (2,)])
+        finally:
+            await self.con.execute('ROLLBACK')
+
     async def test_cursor_02(self):
         st = await self.con.prepare('SELECT generate_series(0, 20)')
         async with self.con.transaction():