diff --git a/packages/types/lib/src/market_price.dart b/packages/types/lib/src/market_price.dart
index 00829ae5..c22576f1 100644
--- a/packages/types/lib/src/market_price.dart
+++ b/packages/types/lib/src/market_price.dart
@@ -1,5 +1,3 @@
-import 'dart:convert';
-
 import 'package:meta/meta.dart';
 import 'package:types/price.dart';
 import 'package:types/types.dart';
@@ -112,7 +110,4 @@ class MarketPrice extends PriceBase<TradeSymbol> {
 
   /// The symbol of the trade good.
   TradeSymbol get tradeSymbol => symbol;
-
-  @override
-  String toString() => jsonEncode(toJson());
 }
diff --git a/packages/types/test/src/market_price_test.dart b/packages/types/test/src/market_price_test.dart
index be80bfa8..be97d206 100644
--- a/packages/types/test/src/market_price_test.dart
+++ b/packages/types/test/src/market_price_test.dart
@@ -21,4 +21,26 @@ void main() {
     expect(price2.hashCode, price.hashCode);
     expect(json2, json);
   });
+
+  test('MarketPrice.copyWith', () {
+    final moonLanding = DateTime.utc(1969, 7, 20, 20, 18, 04);
+    final price = MarketPrice(
+      waypointSymbol: WaypointSymbol.fromString('S-A-W'),
+      symbol: TradeSymbol.FUEL,
+      supply: SupplyLevel.ABUNDANT,
+      purchasePrice: 1,
+      sellPrice: 2,
+      tradeVolume: 10,
+      timestamp: moonLanding,
+      activity: ActivityLevel.WEAK,
+    );
+    // Only sellPrice is currently supported.
+    final price2 = price.copyWith(
+      sellPrice: 4,
+    );
+    expect(price2.purchasePrice, 1);
+    expect(price2.sellPrice, 4);
+    expect(price2.tradeVolume, 10);
+    expect(price2.activity, ActivityLevel.WEAK);
+  });
 }