It　is　known　that　the　performance　of　traditional　passive　tuned　mass　dampers　(TMDs)　is　highly　sensitive　to　vibration　frequency.　The　fundamental　frequency　of　existing　tall　buildings　may　shift　to　lower　value　due　to　damage　or　other　reasons.　In　this　regard,　this　paper　deals　with　the　resultant　detuning　problems　of　a　traditional　passive　TMD　for　vibration　control　by　retrofitting　it　with　a　passive　adaptive　negative　stiffness　device　(NSD).　The　applied　NSD　not　only　provides　negative　stiffness　for　adjusting　the　TMD＇s　de-tuned　stiffness　at　its　working　stage,　but　also　offers　a　fail-safe　limiting　stop　for　the　TMD　at　large　deformation/stroke.　In　this　study,　compared　to　the　original　TMD,　a　novel　TMD-NSD　assembly　is　proposed　that　is　shown　to　be　more　effective　for　serviced　structures.　For　example,　the　original　TMD　can　only　provide　about　2.83%　additional　damping　ratio　to　frequency-changed　structures,　while　the　newly　proposed　TMD-NSD　further　improves　the　damping　ratio　to　5.34%.　Moreover,　in　the　study　it　is　found　that　the　TMD-NSD　also　outperforms　the　TMD　in　resisting　dynamic　lateral　loading　such　as　along　winds,　cross　winds,　and　earthquakes.