1 files changed, 2 insertions, 2 deletions
diff --git a/histogram.py b/histogram.py
index 993b503..d45e93f 100644
--- a/histogram.py
+++ b/histogram.py
@@ -85,8 +85,8 @@ class SimpleHistogram(Generic[T]):
             return txt
 
         max_label_width: Optional[int] = None
-        lowest_start: int = None
-        highest_end: int = None
+        lowest_start: Optional[int] = None
+        highest_end: Optional[int] = None
         for bucket in sorted(self.buckets, key=lambda x: x[0]):
             start = bucket[0]
             if lowest_start is None: