diff --git a/rmw_zenoh_cpp/src/rmw_zenoh.cpp b/rmw_zenoh_cpp/src/rmw_zenoh.cpp
index 345c7927..d84911de 100644
--- a/rmw_zenoh_cpp/src/rmw_zenoh.cpp
+++ b/rmw_zenoh_cpp/src/rmw_zenoh.cpp
@@ -81,17 +81,8 @@ namespace
 // careful about who owns the string.
 z_owned_keyexpr_t ros_topic_name_to_zenoh_key(const char * const topic_name, size_t domain_id)
 {
-  std::string d = std::to_string(domain_id);
-
-  size_t start_offset = 0;
-  size_t topic_name_len = strlen(topic_name);
-  size_t end_offset = topic_name_len;
-
-  const std::string mangled_topic_name = liveliness::mangle_name(topic_name);
-
-  return z_keyexpr_join(
-    z_keyexpr(d.c_str()),
-    z_keyexpr(mangled_topic_name.c_str()));
+  const std::string keyexpr_str = std::to_string(domain_id) + "/" + liveliness::mangle_name(topic_name);
+  return z_keyexpr_new(keyexpr_str.c_str());
 }
 
 //==============================================================================