diff --git a/src/ChibiRuby.Serializer/Resolvers/GeneratedResolver.cs b/src/ChibiRuby.Serializer/Resolvers/GeneratedResolver.cs
index a23bb8d2..5da7d254 100644
--- a/src/ChibiRuby.Serializer/Resolvers/GeneratedResolver.cs
+++ b/src/ChibiRuby.Serializer/Resolvers/GeneratedResolver.cs
@@ -26,8 +26,9 @@ static Cache()
 
     static bool TryInvokeRegisterFormatter(Type type)
     {
-        if (type.GetCustomAttribute<MRubyObjectAttribute>() == null) return false;
-
+        // Do not gate on [MRubyObject] here: Unity 6000.5+'s linker strips instances of
+        // PreserveAttribute-derived attributes from player builds, so the attribute can be
+        // absent at runtime even for generated types. The generated method is the reliable signal.
         var m = type.GetMethod("__RegisterMRubyValueFormatter",
             BindingFlags.Public |
             BindingFlags.NonPublic |
diff --git a/tests/ChibiRuby.Serializer.Tests/Classes.cs b/tests/ChibiRuby.Serializer.Tests/Classes.cs
index 91ec4e64..f29b9524 100644
--- a/tests/ChibiRuby.Serializer.Tests/Classes.cs
+++ b/tests/ChibiRuby.Serializer.Tests/Classes.cs
@@ -25,3 +25,24 @@ partial struct Struct1
 {
     public long Id { get; set; }
 }
+
+// Simulates a source-generated [MRubyObject] type after Unity 6000.5's linker has stripped the
+// attribute instance (#199): the generated registration method exists, but the attribute does not.
+class AttributeStrippedObject
+{
+    public int Value { get; set; }
+
+    public static void __RegisterMRubyValueFormatter()
+    {
+        GeneratedResolver.Register(new AttributeStrippedObjectFormatter());
+    }
+
+    class AttributeStrippedObjectFormatter : IMRubyValueFormatter<AttributeStrippedObject?>
+    {
+        public MRubyValue Serialize(AttributeStrippedObject? value, MRubyState mrb, MRubyValueSerializerOptions options)
+            => value is null ? default : new MRubyValue(value.Value);
+
+        public AttributeStrippedObject? Deserialize(MRubyValue value, MRubyState mrb, MRubyValueSerializerOptions options)
+            => new() { Value = checked((int)value.IntegerValue) };
+    }
+}
diff --git a/tests/ChibiRuby.Serializer.Tests/GeneratedFormatterTest.cs b/tests/ChibiRuby.Serializer.Tests/GeneratedFormatterTest.cs
index 56376185..237e317d 100644
--- a/tests/ChibiRuby.Serializer.Tests/GeneratedFormatterTest.cs
+++ b/tests/ChibiRuby.Serializer.Tests/GeneratedFormatterTest.cs
@@ -95,4 +95,16 @@ public void DeserializeWithCtor()
         Assert.That(result.Y, Is.EqualTo(456));
         Assert.That(result.Hoge, Is.EqualTo("hello hello"));
     }
+
+    [Test]
+    public void RegisterFormatterWithoutAttributeInstance()
+    {
+        // The [MRubyObject] attribute instance may be stripped by Unity 6000.5+'s linker (#199).
+        // Registration must work based on the generated method alone.
+        var result = MRubyValueSerializer.Deserialize<AttributeStrippedObject>(new MRubyValue(42), state)!;
+        Assert.That(result.Value, Is.EqualTo(42));
+
+        var serialized = MRubyValueSerializer.Serialize(new AttributeStrippedObject { Value = 43 }, state);
+        Assert.That(serialized, Is.EqualTo(new MRubyValue(43)));
+    }
 }