Though much attention has been given to the neural structures that underlie the long-term consolidation of contextual memories, little is known about the mechanisms responsible for the maintenance of memory precision. Here, we demonstrate a rapid time-dependent decline in memory precision in GABAB(1a) receptor knockout mice. First, we show that GABAB(1a) receptors are required for the maintenance, but not encoding, of a precise fear memory. We then demonstrate that GABAB(1a) receptors are required for the maintenance, but not encoding, of spatial memories. Our findings suggest that GABA-mediated presynaptic inhibition regulates the maintenance of memory precision as a function of memory age.