diff --git a/README.md b/README.md
index 9b0648b..0f1feb0 100644
--- a/README.md
+++ b/README.md
@@ -296,6 +296,8 @@ The goal is to validate roto's implementation against the Proto3 specification.
 
 ### Unsupported Features
 
+- **Default Values**: Missing fields return `RotoError::FieldNotFound` instead of the Proto3 default value (e.g., `0` or `""`).
+- **Field Presence**: No `has_field()` methods are generated to distinguish between a field being absent and a field being set to its default value.
 - **`oneof` Fields**: Not currently supported in code generation.
 - **`map` Fields**: Not currently supported.
 - **Packed Repeated Fields**: `roto` expects individual tags for all repeated elements; it does not support the packed encoding used for scalar numeric types in Proto3.