We show that from an appropriate manipulation of the biconfluent Heun differential equation one can obtain the correct expression for the energy eigenvalues for the Klein–Gordon equation without potential in the background of Som–Raychaudhuri space-time with a cosmic string as a particular case (kL= 0 ) of Vitória et al. (Eur Phys J C 78(1):44, 2018), in opposition what was stated in a recent paper published in this journal (Ahmed in Eur Phys J C 79(8):682, 2019). In a recent paper in this journal, Ahmed [1] has pointed out an incorrect expression in [2]. The author has solved the Klein–Gordon equation without interaction in the Som–Raychaudhuri space-time with the cosmic string using the Nikiforov–Uvarov method and obtained the energy eigenvalues and the corresponding eigenfunctions of the system. The problem solved in [1] is a special case associated to kL = 0 in Ref. [2]. Ahmed has claimed that to obtain the correct result, one should start from Eq. (4) but not from the condition (12), which is obtained from the biconfluent Heun equation (10). The purpose of this comment is to show that following an appropriate manipulation of the biconfluent Heun equation, the correct energy eigenvalues for kL = 0 can be obtained as a particular case of [2], as opposed to what was advertised in Ref. [1].