diff --git a/neo.UnitTests/UT_FifoSet.cs b/neo.UnitTests/UT_FifoSet.cs
index 218aeefde2..f1c611bdfa 100644
--- a/neo.UnitTests/UT_FifoSet.cs
+++ b/neo.UnitTests/UT_FifoSet.cs
@@ -27,6 +27,28 @@ public void FifoSetTest()
             Assert.IsTrue(set.Add(c));
 
             CollectionAssert.AreEqual(set.ToArray(), new UInt256[] { a, c });
+            
+                        var d = new UInt256(new byte[32] {
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x02
+            });
+
+            // Testing Fifo max size
+            Assert.IsTrue(set.Add(d));
+            CollectionAssert.AreEqual(set.ToArray(), new UInt256[] { a, c, d });
+
+            var e = new UInt256(new byte[32] {
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+                0x01, 0x03
+            });
+
+            Assert.IsTrue(set.Add(e));
+            Assert.IsFalse(set.Add(e));
+            CollectionAssert.AreEqual(set.ToArray(), new UInt256[] { c, d, e });
         }
     }
 }