diff --git a/iceoryx2-ffi/cxx/include/iox2/unique_port_id.hpp b/iceoryx2-ffi/cxx/include/iox2/unique_port_id.hpp
index 616bdfffe..cc423795f 100644
--- a/iceoryx2-ffi/cxx/include/iox2/unique_port_id.hpp
+++ b/iceoryx2-ffi/cxx/include/iox2/unique_port_id.hpp
@@ -31,7 +31,7 @@ class UniquePublisherId {
     auto operator=(UniquePublisherId&& rhs) noexcept -> UniquePublisherId&;
     ~UniquePublisherId();
 
-    auto bytes() -> iox::optional<RawIdType>&;
+    auto bytes() -> const iox::optional<RawIdType>&;
 
   private:
     template <ServiceType, typename, typename>
@@ -56,7 +56,7 @@ class UniqueSubscriberId {
     auto operator=(UniqueSubscriberId&& rhs) noexcept -> UniqueSubscriberId&;
     ~UniqueSubscriberId();
 
-    auto bytes() -> iox::optional<RawIdType>&;
+    auto bytes() -> const iox::optional<RawIdType>&;
 
   private:
     template <ServiceType, typename, typename>
@@ -80,7 +80,7 @@ class UniqueNotifierId {
     auto operator=(UniqueNotifierId&& rhs) noexcept -> UniqueNotifierId&;
     ~UniqueNotifierId();
 
-    auto bytes() -> iox::optional<RawIdType>&;
+    auto bytes() -> const iox::optional<RawIdType>&;
 
   private:
     template <ServiceType>
@@ -104,7 +104,7 @@ class UniqueListenerId {
     auto operator=(UniqueListenerId&& rhs) noexcept -> UniqueListenerId&;
     ~UniqueListenerId();
 
-    auto bytes() -> iox::optional<RawIdType>&;
+    auto bytes() -> const iox::optional<RawIdType>&;
 
   private:
     template <ServiceType>
diff --git a/iceoryx2-ffi/cxx/src/unique_port_id.cpp b/iceoryx2-ffi/cxx/src/unique_port_id.cpp
index cb354703e..07b07409a 100644
--- a/iceoryx2-ffi/cxx/src/unique_port_id.cpp
+++ b/iceoryx2-ffi/cxx/src/unique_port_id.cpp
@@ -43,7 +43,7 @@ UniquePublisherId::UniquePublisherId(iox2_unique_publisher_id_h handle)
     : m_handle { handle } {
 }
 
-auto UniquePublisherId::bytes() -> iox::optional<RawIdType>& {
+auto UniquePublisherId::bytes() -> const iox::optional<RawIdType>& {
     if (!m_raw_id.has_value() && m_handle != nullptr) {
         RawIdType bytes { UNIQUE_PORT_ID_LENGTH, 0 };
         iox2_unique_publisher_id_value(m_handle, bytes.data(), bytes.size());
@@ -90,7 +90,7 @@ UniqueSubscriberId::UniqueSubscriberId(iox2_unique_subscriber_id_h handle)
     : m_handle { handle } {
 }
 
-auto UniqueSubscriberId::bytes() -> iox::optional<RawIdType>& {
+auto UniqueSubscriberId::bytes() -> const iox::optional<RawIdType>& {
     if (!m_raw_id.has_value() && m_handle != nullptr) {
         RawIdType bytes { UNIQUE_PORT_ID_LENGTH, 0 };
         iox2_unique_subscriber_id_value(m_handle, bytes.data(), bytes.size());
@@ -136,7 +136,7 @@ UniqueNotifierId::UniqueNotifierId(iox2_unique_notifier_id_h handle)
     : m_handle { handle } {
 }
 
-auto UniqueNotifierId::bytes() -> iox::optional<RawIdType>& {
+auto UniqueNotifierId::bytes() -> const iox::optional<RawIdType>& {
     if (!m_raw_id.has_value() && m_handle != nullptr) {
         RawIdType bytes { UNIQUE_PORT_ID_LENGTH, 0 };
         iox2_unique_notifier_id_value(m_handle, bytes.data(), bytes.size());
@@ -182,7 +182,7 @@ UniqueListenerId::UniqueListenerId(iox2_unique_listener_id_h handle)
     : m_handle { handle } {
 }
 
-auto UniqueListenerId::bytes() -> iox::optional<RawIdType>& {
+auto UniqueListenerId::bytes() -> const iox::optional<RawIdType>& {
     if (!m_raw_id.has_value() && m_handle != nullptr) {
         RawIdType bytes { UNIQUE_PORT_ID_LENGTH, 0 };
         iox2_unique_listener_id_value(m_handle, bytes.data(), bytes.size());