diff --git a/Command.py b/Command.py
index 3a8927e..18b9435 100644
--- a/Command.py
+++ b/Command.py
@@ -65,7 +65,8 @@ class Command:
         if dt.lower() == "yesterday":
             today = datetime.today()
             y = today - timedelta(days = 1)
-            self.time.replace(year = y.year, month = y.month, day = y.day)
+            self.time = self.time.replace(
+                    year = y.year, month = y.month, day = y.day)
             return True
         m = re.match('^(?:(\d{4})[-/])?(\d{1,2})[-/](\d{1,2})$', dt)
         if m is not None: