We argue that there is a need for Multi-Tenant Customizable OLTP systems. Such systems need a Multi-Tenant Customizable Database (MTC-DB) as a backing. To stimulate the development of such databases, we propose the benchmark MTCB. Benchmarks for OLTP exist and multi-tenant benchmarks exist, but no MTC-DB benchmark exists that accounts for customizability. We formulate seven requirements for the benchmark: realistic, unambiguous, comparable, correct, scalable, simple and independent. It focuses on performance aspects and produces nine metrics: Aulbach compliance, size on disk, tenants created, types created, attributes created, transaction data type instances created per minute, transaction data type instances loaded by ID per minute, conjunctive searches per minute and disjunctive searches per minute. We present a specification and an example implementation in Java 8, which can be accessed on this public repository: https://bitbucket.org/actfact/mtcdb-benchmark. In the same repository a naive implementation can be found of an MTC-DB where each tenant has its own schema. We believe that this benchmark is a valuable contribution to the community of MTC-DB developers, because it provides objective comparability as well as a precise definition of the concept of MTC-DB.