diff --git a/src/message.rs b/src/message.rs
index 11a399a..1e27912 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -188,7 +188,7 @@ impl Protocol300Message {
             return Err(MessageDecodingError::LengthMismatch());
         }
 
-        let message_identifier = match MessageIdentifier::try_from(bytes[2]) {
+        let message_identifier = match MessageIdentifier::try_from(bytes[2] & 0x0F) {
             Ok(id) => id,
             Err(e) => {
                 error!("Failed to decode message: invalid message identifier byte 0x{:02X}", bytes[2]);
@@ -196,7 +196,7 @@ impl Protocol300Message {
             }
         };
         
-        let function_code = match FunctionCode::try_from(bytes[3]) {
+        let function_code = match FunctionCode::try_from(bytes[3] & 0x0F) {
             Ok(fc) => fc,
             Err(e) => {
                 error!("Failed to decode message: invalid function code byte 0x{:02X}", bytes[3]);