diff --git a/jafgen/simulation.py b/jafgen/simulation.py
index a6a87a3..4a5a94c 100644
--- a/jafgen/simulation.py
+++ b/jafgen/simulation.py
@@ -107,13 +107,13 @@ def run_simulation(self):
         ):
             for market in self.markets:
                 day = Day(i)
-                for result in market.sim_day(day):
-                    if result is not None and all(val is not None for val in result):
-                        order, tweet = result
+                for order, tweet in market.sim_day(day):
+                    if order:
                         self.orders.append(order)
-                        self.tweets.append(tweet)
                         if order.customer.customer_id not in self.customers:
                             self.customers[order.customer.customer_id] = order.customer
+                    if tweet:
+                        self.tweets.append(tweet)
 
     def save_results(self) -> None:
         stock: Stock = Stock()
diff --git a/jafgen/stores/market.py b/jafgen/stores/market.py
index 740c027..792c5cc 100644
--- a/jafgen/stores/market.py
+++ b/jafgen/stores/market.py
@@ -1,4 +1,5 @@
 import random
+from typing import Iterator
 
 import numpy as np
 
@@ -6,10 +7,12 @@
     BrunchCrowd,
     Casuals,
     Commuter,
+    HealthNut,
     RemoteWorker,
     Student,
-    HealthNut,
 )
+from jafgen.customers.order import Order
+from jafgen.customers.tweet import Tweet
 
 
 class Market(object):
@@ -38,10 +41,10 @@ def __init__(self, store, num_customers, days_to_penetration=365):
 
         self.active_customers = []
 
-    def sim_day(self, day):
+    def sim_day(self, day) -> Iterator[tuple[Order | None, Tweet | None]]:
         days_since_open = self.store.days_since_open(day)
         if days_since_open < 0:
-            yield None
+            yield None, None
             return
         elif days_since_open < 7:
             pct_penetration = min(days_since_open / self.days_to_penetration, 1)
@@ -53,7 +56,7 @@ def sim_day(self, day):
         num_desired_customers = market_penetration * len(self.addressable_customers)
         customers_to_add = int(num_desired_customers - len(self.active_customers))
 
-        for i in range(customers_to_add):
+        for _ in range(customers_to_add):
             customer = self.addressable_customers.pop()
             self.active_customers.append(customer)