A series of flume-based experiments was undertaken to investigate the effect of below-threshold antecedent flow conditions on the stability of a graded sediment bed (D16 = 1.8 mm, D50 = 4.8 mm, D84 = 7.8 mm, and σg = 2.08). The experiments revealed that stability is dependent not only on the applied shear stress of the antecedent flow (1.46, 2.08, 2.19, 2.41, and 2.63 N m-2) but also on its duration (0, 15, 30, 60, 1440 and 5760 min). A new stability diagram has been developed to illustrate stress history effects for the graded substrates and hydraulic conditions used in the investigation. The diagram has implications for flume-based experimental practice, the prediction of sediment transport rates, and sediment management in river restoration.