https://github.com/php-memcached-dev/php-memcached/commit/09e29e65deabae5b23fdf5db1928992d6107d9c9#diff-f76062ebbcf30f0491af9ca937d17762R2874 ZSTR_VAL(str) == 0 should be ZSTR_LEN(str) == 0 Added fix and testcase.