Some groups of fossil beetles are difficult to study because the characters needed for identification or classification are hidden and difficult to study. Ptinidae is one of these groups. We describe herein Cretasernus spinosus gen. et sp. nov. (Coleoptera: Ptinidae) based on one fossil specimen, the only known specimen of this family from Kachin amber (mid-Cretaceous of Myanmar). The holotype was imaged using an X-ray micro-CT system to obtain high-quality 3D images to complement the structures visualized using optical microscopes. The new species shows two autapomorphic characters never described in any extant or extinct species in this family: a groove near the base of the 11th antennomere, which makes it appear as a much smaller additional antennomere, and transverse metacoxae touching at the middle. Phylogenetic analysis of the new species clearly supports this new genus as part of Anobiidae sensu stricto (i.e. excluding the spider beetles) despite antennae that are certainly more similar to those seen in the many of the spider beetles (except for the modified 11th antennomere). Some of the extant species in this family are wood-borers and the involvement of beetles in resin production during the Cretaceous is a hypothesis that is suggested often. However, some ideas against the involvement of Ptinidae in resin production within the mid-Cretaceous forests of Myanmar are discussed.