- xbt_assert(mutex->get_owner() == issuer,
- "Actor %s cannot wait on ConditionVariable %p since it does not own the provided mutex %p",
- issuer->get_cname(), this, mutex);
+ auto* owner = mutex->get_owner();
+ xbt_assert(owner == issuer,
+ "Actor %s cannot wait on ConditionVariable %p since it does not own the provided mutex %p (which is "
+ "owned by %s).",
+ issuer->get_cname(), this, mutex, (owner == nullptr ? "nobody" : owner->get_cname()));