diff --git a/requests_mock/mocker.py b/requests_mock/mocker.py
index bf207aa..186fbb9 100644
--- a/requests_mock/mocker.py
+++ b/requests_mock/mocker.py
@@ -62,7 +62,10 @@ class MockerCore(object):
 
     def __init__(self, **kwargs):
         self.case_sensitive = kwargs.pop('case_sensitive', self.case_sensitive)
-        self._adapter = adapter.Adapter(case_sensitive=self.case_sensitive)
+        self._adapter = (
+            kwargs.pop('adapter', None) or
+            adapter.Adapter(case_sensitive=self.case_sensitive)
+        )
 
         self._real_http = kwargs.pop('real_http', False)
         self._last_send = None