Achieving secure high-performance implementations for constrained applications such as implantable and wearable medical devices are a priority in efficient block ciphers. However, security of these algorithms is not guaranteed in the presence of malicious and natural faults. Recently, a new lightweight block cipher, Midori, has been proposed that optimizes the energy consumption besides having low latency and hardware complexity. In this paper, fault diagnosis schemes for variants of Midori are proposed. To the best of the authors’ knowledge, there has been no fault diagnosis scheme presented in the literature for Midori to date. The fault diagnosis schemes are provided for the nonlinear S-box layer and for the round structures with both 64-bit and 128-bit Midori symmetric key ciphers. The proposed schemes are benchmarked on a field-programmable gate array and their error coverage is assessed with fault-injection simulations. These proposed error detection architectures make the implementations of this new low-energy lightweight block cipher more reliable.