Add the following test case to HashSet.cpp in WTF tests: TEST(WTF, HashSetFindZero) { HashSet<uint64_t> testSet; // Initial capacity is null. ASSERT_EQ(0, testSet.capacity()); testSet.add(static_cast<uint64_t>(123)); testSet.add(static_cast<uint64_t>(456)); ASSERT_TRUE(testSet.find(static_cast<uint64_t>(0)) == testSet.end()); } You'll hit an assertion in template<typename Key, typename Value, typename Extractor, typename HashFunctions, typename Traits, typename KeyTraits> template<typename HashTranslator, typename T> void HashTable<Key, Value, Extractor, HashFunctions, Traits, KeyTraits>::checkKey(const T& key) { if (!HashFunctions::safeToCompareToEmptyOrDeleted) return; ASSERT(!HashTranslator::equal(KeyTraits::emptyValue(), key)); This results in HashSet::find returning a bogus iterator and HashSet::remove deleting an unrelated item, resulting in a really bad consistent state where size can be a bogus value like -1.