diff --git a/testtools/matchers/_impl.py b/testtools/matchers/_impl.py
index 888d8ee..19a93af 100644
--- a/testtools/matchers/_impl.py
+++ b/testtools/matchers/_impl.py
@@ -114,7 +114,7 @@ class MismatchError(AssertionError):
     # characters are in the matchee, matcher or mismatch.
 
     def __init__(self, matchee, matcher, mismatch, verbose=False):
-        super(AssertionError, self).__init__(self)
+        super(MismatchError, self).__init__()
         self.matchee = matchee
         self.matcher = matcher
         self.mismatch = mismatch