diff --git a/rmw_fastrtps_cpp/src/rmw_serialize.cpp b/rmw_fastrtps_cpp/src/rmw_serialize.cpp
index 4dc5645ac..dd954efcc 100644
--- a/rmw_fastrtps_cpp/src/rmw_serialize.cpp
+++ b/rmw_fastrtps_cpp/src/rmw_serialize.cpp
@@ -89,4 +89,14 @@ rmw_deserialize(
   delete tss;
   return ret == true ? RMW_RET_OK : RMW_RET_ERROR;
 }
+
+rmw_ret_t
+rmw_get_serialized_message_size(
+  const rosidl_message_type_support_t * /*type_support*/,
+  const rosidl_message_bounds_t * /*message_bounds*/,
+  size_t * /*size*/)
+{
+  RMW_SET_ERROR_MSG("unimplemented");
+  return RMW_RET_ERROR;
+}
 }  // extern "C"
diff --git a/rmw_fastrtps_cpp/src/rmw_subscription.cpp b/rmw_fastrtps_cpp/src/rmw_subscription.cpp
index a51fa5826..395c17448 100644
--- a/rmw_fastrtps_cpp/src/rmw_subscription.cpp
+++ b/rmw_fastrtps_cpp/src/rmw_subscription.cpp
@@ -46,10 +46,7 @@ rmw_init_subscription_allocation(
 {
   (void) type_support;
   (void) message_bounds;
-  // Since this feature is currently not implemented in FastRTPS, set the
-  // allocation pointer to NULL. The downstream `rmw_take` methods will
-  // ignore the value.
-  allocation = nullptr;
+  (void) allocation;
   return RMW_RET_OK;
 }
 
diff --git a/rmw_fastrtps_dynamic_cpp/src/rmw_serialize.cpp b/rmw_fastrtps_dynamic_cpp/src/rmw_serialize.cpp
index 64efe0910..5e67c73a9 100644
--- a/rmw_fastrtps_dynamic_cpp/src/rmw_serialize.cpp
+++ b/rmw_fastrtps_dynamic_cpp/src/rmw_serialize.cpp
@@ -88,4 +88,14 @@ rmw_deserialize(
   delete tss;
   return ret == true ? RMW_RET_OK : RMW_RET_ERROR;
 }
+
+rmw_ret_t
+rmw_get_serialized_message_size(
+  const rosidl_message_type_support_t * /*type_support*/,
+  const rosidl_message_bounds_t * /*message_bounds*/,
+  size_t * /*size*/)
+{
+  RMW_SET_ERROR_MSG("unimplemented");
+  return RMW_RET_ERROR;
+}
 }  // extern "C"