The main goal of Network Coding (NC) is to find an optimal transmission of data in a network. NC presents an advantage for wireless sensor networks (WSNs) in term of network lifetime. However, the Network Coding-enabled WSNs are affected by various attacks, such as pollution attacks. Many HMAC schemes have been proposed in the literature to secure packets against pollution attacks. In 2015, Esfahani et al. proposed a dual-homomorphic MAC scheme based to the construction of two different MACs to ensure the integrity of coded packets. Their solution has many weaknesses in terms of security against tag pollution attacks. In this paper, we improve their scheme by proposing a novel HMAC scheme for NC enabled WSNs, called E-HMAC, based on multi-linear space to check the integrity of coded packets. The simulation results demonstrate the ability of our proposed scheme to secure the coded packets with a low key storage overhead and communication overhead, compared to Esfahani et al.'s scheme.