Bacterial endospores are encased in a thick layer of specialized peptidoglycan called the cortex that is essential for core dehydration and heat resistance. Spore germination and outgrowth require cortex degradation by enzymes that are deposited in the spore during sporulation. How these enzymes are held inactive during dormancy and activated during germination remains poorly understood. In IMPORTANCE: Bacterial spores are among the most resilient cell types in nature. Their ability to resist sterilization during dormancy yet rapidly germinate and resume growth is central to the transmission and pathogenesis of spore-forming pathogens. A key component of their resistance is a thick layer of specialized peptidoglycan called the cortex that encases them. The cortex maintains the spore core in a highly desiccated state by physically restricting its expansion. Germination and outgrowth require the degradation of this essential envelope layer. The enzymes responsible for cortex degradation are deposited in the spore during sporulation. How these lytic enzymes are held inactive during dormancy has been a longstanding question. One of these enzymes, SleB, is encoded in the same operon as its putative regulator YpeB. Here, we provide biochemical and genetic evidence that YpeB interacts with and inhibits SleB during dormancy. These findings lay the groundwork for elucidating how SleB is activated during germination.