diff --git a/anki/stats.py b/anki/stats.py
index 0430c6fb9..eb0fb9cc2 100644
--- a/anki/stats.py
+++ b/anki/stats.py
@@ -291,6 +291,7 @@ group by day order by day""" % (self._limit(), lim),
             xaxis=dict(tickDecimals=0, max=0.5),
             yaxes=[dict(min=0), dict(position="right", min=0)])
         if days is not None:
+            # pylint: disable=invalid-unary-operand-type
             conf['xaxis']['min'] = -days+0.5
         def plot(id, data, ylabel, ylabel2):
             return self._graph(
@@ -322,6 +323,7 @@ group by day order by day""" % (self._limit(), lim),
             xaxis=dict(tickDecimals=0, max=0.5),
             yaxes=[dict(min=0), dict(position="right", min=0)])
         if days is not None:
+            # pylint: disable=invalid-unary-operand-type
             conf['xaxis']['min'] = -days+0.5
         def plot(id, data, ylabel, ylabel2):
             return self._graph(