diff --git a/test/transaction_size_test.dart b/test/transaction_size_test.dart
new file mode 100644
index 0000000..2eac8d1
--- /dev/null
+++ b/test/transaction_size_test.dart
@@ -0,0 +1,37 @@
+import 'package:test/test.dart';
+import '../lib/src/transaction.dart';
+
+main() {
+
+  group('Transaction.txSize', () {
+
+    test('transaction size is not 1 byte under', () {
+
+      // Taken from
+      // 471b4cfb93d94c74d7f8a3f6b4e877502d6deeba6902086be342b80386342a46 which
+      // supposedly has the incorrect size
+
+      final tx = Transaction.fromHex(
+        '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'
+      );
+
+      expect(tx.txSize, 310);
+
+    });
+
+    test('transaction is not 1 byte over', () {
+
+      // Taken from 8de5e69a1f306ab64242b576d7de2ae03645df93f6b07acf5ce392eb9ed3ce28
+      // Supposedly overpays 20 satoshis
+
+      final tx = Transaction.fromHex(
+        '0300000001185117b997598905fb7eb8caf144f80ac929bb446dc0ad30bcdd22e502d38d4f010000006a47304402201859cb81611f3af1ad6389c6d2c9f9cbbd6dd683cd5de84da1cd38447df14648022028c2a5827c221cfeaa9e77a24eeb6bdc9693ff172db82165a02e4ccb85d1c3b30121027c447812d54c147b61cb1f7947bee25adcb40787c795f240bd91e912b12ccb28ffffffff0300000000000000001976a914b8be9179431a4ffd394589426ec802648bdc4d9e88ac06264c00000000001976a9146dc10797a388d19bbd64d82f814cf174c0379ca288ac0000000000000000166a14476f64206a756c20667261204e6f726765203a2900000000'
+      );
+
+      expect(tx.txSize, 256);
+
+    });
+
+  });
+
+}