diff --git a/Substrate.NetApi.Test/TypeConverters/PrimitiveTypesTest.cs b/Substrate.NetApi.Test/TypeConverters/PrimitiveTypesTest.cs
index 6c554e9..51ee925 100644
--- a/Substrate.NetApi.Test/TypeConverters/PrimitiveTypesTest.cs
+++ b/Substrate.NetApi.Test/TypeConverters/PrimitiveTypesTest.cs
@@ -184,6 +184,19 @@ public void PrimU128Test()
             Assert.AreEqual(value, primImplicit);
         }
 
+        /// <summary>
+        /// From real use case here : https://mythos.subscan.io/block/2826170?tab=event&event=2826170-189
+        /// </summary>
+        [Test]
+        [TestCase("310789037729451024594500450253905211276")]
+        public void PrimU128_FromMaxBigIntegerValue_Test(string valueStr)
+        {
+            var value = BigInteger.Parse(valueStr);
+
+            var prim = new U128(value);
+            Assert.That(prim.Value, Is.EqualTo(value));
+        }
+
         [Test]
         public void PrimU128CreateTest()
         {
@@ -213,6 +226,22 @@ public void PrimU128_WithNegativeNumber_ShouldFail()
             Assert.Throws<InvalidOperationException>(() => new U128(number));
         }
 
+        [Test]
+        public void PrimU256_MaxValue()
+        {
+            BigInteger u256Max = BigInteger.Pow(2, 256) - 1;
+            var u256 = new U256(u256Max);
+
+            Assert.That(u256.Value, Is.EqualTo(u256Max));
+        }
+
+        [Test]
+        public void PrimU256_BasicNumberTest()
+        {
+            var u256 = new U256(new BigInteger(10));
+            Assert.That(u256.Value, Is.EqualTo(new BigInteger(10)));
+        }
+
         [Test]
         public void PrimU256Test()
         {
diff --git a/Substrate.NetApi/Model/Types/Primitive/U128.cs b/Substrate.NetApi/Model/Types/Primitive/U128.cs
index 51e3ed2..be8bd2e 100644
--- a/Substrate.NetApi/Model/Types/Primitive/U128.cs
+++ b/Substrate.NetApi/Model/Types/Primitive/U128.cs
@@ -91,13 +91,20 @@ public override void Create(BigInteger value)
 
             var byteArray = value.ToByteArray();
 
-            if (byteArray.Length > TypeSize)
+            if (byteArray.Length > TypeSize + 1)
             {
                 throw new NotSupportedException($"Wrong byte array size for {TypeName()}, max. {TypeSize} bytes!");
             }
 
             var bytes = new byte[TypeSize];
-            byteArray.CopyTo(bytes, 0);
+            if (byteArray.Length == TypeSize + 1)
+            {
+                Array.Copy(byteArray, 0, bytes, 0, TypeSize);
+            }
+            else
+            {
+                byteArray.CopyTo(bytes, 0);
+            }
             Bytes = bytes;
             Value = value;
         }
diff --git a/Substrate.NetApi/Model/Types/Primitive/U256.cs b/Substrate.NetApi/Model/Types/Primitive/U256.cs
index 633174c..efec4a9 100644
--- a/Substrate.NetApi/Model/Types/Primitive/U256.cs
+++ b/Substrate.NetApi/Model/Types/Primitive/U256.cs
@@ -92,14 +92,20 @@ public override void Create(BigInteger value)
                 throw new InvalidOperationException($"Unable to create a {nameof(U256)} instance while value is negative");
 
             var byteArray = value.ToByteArray();
-
-            if (byteArray.Length > TypeSize)
+            
+            if (byteArray.Length > TypeSize + 1)
             {
                 throw new NotSupportedException($"Wrong byte array size for {TypeName()}, max. {TypeSize} bytes!");
             }
 
             var bytes = new byte[TypeSize];
-            byteArray.CopyTo(bytes, 0);
+            if(byteArray.Length == TypeSize + 1) {
+                Array.Copy(byteArray, 0, bytes, 0, TypeSize);
+            }
+            else {
+                byteArray.CopyTo(bytes, 0);
+            }
+            
             Bytes = bytes;
             Value = value;
         }