diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
index 2c1f73547ba2..04c5da0f0996 100755
--- a/lib/matplotlib/dates.py
+++ b/lib/matplotlib/dates.py
@@ -707,7 +707,7 @@ def __call__(self, x, pos=None):
         elif six.callable(fmt):
             result = fmt(x, pos)
         else:
-            raise TypeError('Unexpected type passed to {!r}.'.formatter(self))
+            raise TypeError('Unexpected type passed to {0!r}.'.format(self))
 
         return result