Using high-resolution, high quality spectra we investigate the presence of $^6$Li in two lithium-poor stars that host extrasolar planetary systems. We present improved atomic and molecular line lists for the region in the vicinity of the lithium line at 6707.8 Å, and we produce an excellent fit to the solar spectrum. From line profile fitting, we find results consistent with no $^6$Li in either of the lithium-poor planet-bearing stars or in three comparison stars with and without planets, and 1-$σ$ upper limits of 0.04 for the isotopic ratios of the two lithium-poor stars give an upper limit of 0.3 Jupiter masses of material with primordial abundances that could have been recently deposited in their outer layers. Our results suggest that post-main sequence accretion of planets or planetary material that is undepleted in lithium is uncommon.