diff --git a/src/order_matching/matching_engine.py b/src/order_matching/matching_engine.py
index 3befa84..32f1d11 100644
--- a/src/order_matching/matching_engine.py
+++ b/src/order_matching/matching_engine.py
@@ -106,6 +106,11 @@ def _execute_trades_for_one_price(self, incoming_order: Order, price: float) ->
             if book_order.size == 0:
                 zero_size_orders.append(book_order)
         opposite_side_orders[price].remove(orders=zero_size_orders)
+        for book_order in zero_size_orders:
+            expiration_orders = self.unprocessed_orders.orders_by_expiration[book_order.expiration]
+            expiration_orders.remove(orders=[book_order])
+            if len(expiration_orders) == 0:
+                self.unprocessed_orders.orders_by_expiration.pop(book_order.expiration)
         if len(list(filter(lambda order: order.size > 0, opposite_side_orders[price]))) == 0:
             opposite_side_orders.pop(price)
         return ExecutedTrades(trades=trades)
diff --git a/tests/test_matching_engine.py b/tests/test_matching_engine.py
index fa9f669..c410b36 100644
--- a/tests/test_matching_engine.py
+++ b/tests/test_matching_engine.py
@@ -744,6 +744,57 @@ def test_cancellation_of_expired_orders(self) -> None:
         assert matching_engine.unprocessed_orders.bids == dict()
         assert matching_engine.unprocessed_orders.offers == dict()
 
+    def test_removal_of_filled_orders(self) -> None:
+        matching_engine = MatchingEngine(seed=1)
+        t0 = datetime(2023, 1, 1)
+        buy = LimitOrder(side=Side.BUY, price=100.0, size=10, timestamp=t0, order_id="A", trader_id="x")
+        sell = LimitOrder(
+            side=Side.SELL, price=100.0, size=10, timestamp=t0 + timedelta(seconds=1), order_id="B", trader_id="y"
+        )
+        matching_engine.match(timestamp=t0, orders=Orders([buy]))
+        matching_engine.match(timestamp=t0 + timedelta(seconds=1), orders=Orders([sell]))  # "A" is fully filled
+
+        order_book = matching_engine.unprocessed_orders
+
+        assert order_book.bids == {}
+        assert order_book.offers == {}
+        assert order_book.orders_by_expiration == {}
+
+    def test_live_order_eviction(self) -> None:
+        matching_engine = MatchingEngine(seed=1)
+        timestamp = datetime(2023, 1, 1)
+        expiration = timestamp + timedelta(hours=1)
+
+        # 1) rest "X" @100 with a finite expiration, then fully fill it
+        order = LimitOrder(
+            side=Side.BUY, price=100.0, size=10, timestamp=timestamp, order_id="X", trader_id="x", expiration=expiration
+        )
+        matching_engine.match(timestamp=timestamp, orders=Orders(orders=[order]))
+        order = LimitOrder(
+            side=Side.SELL,
+            price=100.0,
+            size=10,
+            timestamp=timestamp + timedelta(seconds=1),
+            order_id="B",
+            trader_id="y",
+        )
+        matching_engine.match(timestamp=timestamp + timedelta(seconds=1), orders=Orders(orders=[order]))
+
+        # 2) a brand-new LIVE order re-uses id "X" at the same price (default far expiration)
+        order = LimitOrder(
+            side=Side.BUY, price=100.0, size=5, timestamp=timestamp + timedelta(seconds=2), order_id="X", trader_id="z"
+        )
+        matching_engine.match(timestamp=timestamp + timedelta(seconds=2), orders=Orders(orders=[order]))
+
+        # 3) advance time past expiration with any order -> expiry sweep fires
+        order = LimitOrder(
+            side=Side.SELL, price=999.0, size=1, timestamp=timestamp + timedelta(hours=2), order_id="D", trader_id="w"
+        )
+        matching_engine.match(timestamp=timestamp + timedelta(hours=2), orders=Orders(orders=[order]))
+
+        # the live re-used-id "X" was evicted; expected ['X']
+        assert [o.order_id for v in matching_engine.unprocessed_orders.bids.values() for o in v] == ["X"]
+
     def test_matching_with_benchmark(self, random_orders: Orders, benchmark: BenchmarkFixture) -> None:
         order_book = MatchingEngine()
         benchmark(order_book.match, orders=random_orders, timestamp=random_orders.orders[-1].timestamp)