diff --git a/sugartrail/processing.py b/sugartrail/processing.py
index 4aa39c9..b1486da 100644
--- a/sugartrail/processing.py
+++ b/sugartrail/processing.py
@@ -10,7 +10,7 @@ def flatten(d, parent_key='', sep='.'):
     items = []
     for k, v in d.items():
         new_key = parent_key + sep + k if parent_key else k
-        if isinstance(v, collections.MutableMapping):
+        if isinstance(v, collections.abc.MutableMapping):
             items.extend(flatten(v, new_key, sep=sep).items())
         else:
             items.append((new_key, v))