diff --git a/ln.json.tests/JSONTests.cs b/ln.json.tests/JSONTests.cs
index 23dc3c0..02ea47e 100644
--- a/ln.json.tests/JSONTests.cs
+++ b/ln.json.tests/JSONTests.cs
@@ -87,8 +87,6 @@ namespace ln.json.tests
             TestEnumSerialization(testEnum3.C);
             TestEnumSerialization(testEnum3.D);
             TestEnumSerialization(testEnum3.E);
-            
-            
         }
 
         bool TestEnumSerialization(object enumValue)
@@ -105,7 +103,15 @@ namespace ln.json.tests
             return true;
         }
 
-
+        [Test]
+        public void TestMapper()
+        {
+            byte b = 0x80;
+            Assert.IsTrue(JSONMapper.DefaultMapper.Serialize(b, out JSONValue jsonByte));
+            JSONMapper.DefaultMapper.Deserialize(jsonByte, typeof(byte), out object b2);
+            Assert.AreEqual(b,b2);
+            Assert.AreEqual(b.GetType(), b2.GetType());
+        }
 
     }
 }
\ No newline at end of file
diff --git a/ln.json/mapping/JSONMapper.cs b/ln.json/mapping/JSONMapper.cs
index f5cfa11..0517c55 100644
--- a/ln.json/mapping/JSONMapper.cs
+++ b/ln.json/mapping/JSONMapper.cs
@@ -259,7 +259,7 @@ namespace ln.json.mapping
         {
             DefaultMapper.Add(new JSONMapping(
                  typeof(byte),
-                 (JSONMapper arg1, object arg2) => new JSONNumber((int)arg2),
+                 (JSONMapper arg1, object arg2) => new JSONNumber((int)(byte)arg2),
                  (JSONMapper arg1, JSONValue arg2) => Decimal.ToByte(((JSONNumber)arg2).Decimal)
                  ));
             DefaultMapper.Add(new JSONMapping(