diff --git a/aioresponses/core.py b/aioresponses/core.py
index a596259..1a03d20 100644
--- a/aioresponses/core.py
+++ b/aioresponses/core.py
@@ -8,6 +8,7 @@
 from functools import wraps
 from typing import Callable, Dict, Tuple, Union, Optional, List  # noqa
 from unittest.mock import Mock, patch
+from uuid import uuid4
 
 from aiohttp import (
     ClientConnectionError,
@@ -207,7 +208,7 @@ async def build_response(
 
 class aioresponses(object):
     """Mock aiohttp requests made by ClientSession."""
-    _matches = None  # type: List[RequestMatch]
+    _matches = None  # type: Dict[str, RequestMatch]
     _responses = None  # type: List[ClientResponse]
     requests = None  # type: Dict
 
@@ -254,7 +255,7 @@ def clear(self):
 
     def start(self):
         self._responses = []
-        self._matches = []
+        self._matches = {}
         self.patcher.start()
         self.patcher.return_value = self._request_mock
 
@@ -297,7 +298,8 @@ def add(self, url: 'Union[URL, str, Pattern]', method: str = hdrs.METH_GET,
             timeout: bool = False,
             reason: Optional[str] = None,
             callback: Optional[Callable] = None) -> None:
-        self._matches.append(RequestMatch(
+
+        self._matches[str(uuid4())] = (RequestMatch(
             url,
             method=method,
             status=status,
@@ -330,7 +332,7 @@ async def match(
     ) -> Optional['ClientResponse']:
         history = []
         while True:
-            for i, matcher in enumerate(self._matches):
+            for key, matcher in self._matches.items():
                 if matcher.match(method, url):
                     response_or_exc = await matcher.build_response(
                         url, allow_redirects=allow_redirects, **kwargs
@@ -340,7 +342,7 @@ async def match(
                 return None
 
             if matcher.repeat is False:
-                del self._matches[i]
+                del self._matches[key]
 
             if self.is_exception(response_or_exc):
                 raise response_or_exc
diff --git a/tests/test_aioresponses.py b/tests/test_aioresponses.py
index c208a1b..f25c343 100644
--- a/tests/test_aioresponses.py
+++ b/tests/test_aioresponses.py
@@ -2,6 +2,7 @@
 import asyncio
 import re
 from asyncio import CancelledError, TimeoutError
+from random import uniform
 from typing import Coroutine, Generator, Union
 from unittest.mock import patch
 
@@ -482,6 +483,24 @@ async def test_exception_requests_are_tracked(self, mocked):
         self.assertEqual(request.args, ())
         self.assertEqual(request.kwargs, kwargs)
 
+    async def test_possible_race_condition(self):
+        async def random_sleep_cb(url, **kwargs):
+            await asyncio.sleep(uniform(0.1, 1))
+            return CallbackResult(body='test')
+
+        with aioresponses() as mocked:
+            for i in range(20):
+                mocked.get(
+                    'http://example.org/id-{}'.format(i),
+                    callback=random_sleep_cb
+                )
+
+            tasks = [
+                self.session.get('http://example.org/id-{}'.format(i)) for
+                i in range(20)
+            ]
+            await asyncio.gather(*tasks)
+
 
 class AIOResponsesRaiseForStatusSessionTestCase(AsyncTestCase):
     """Test case for sessions with raise_for_status=True.