The quantized current steps produced by a dynamic quantum dot (QD) operated with an external rf signal follow the relation I = nef, where n is the number of electrons captured in the QD, e is the elementary charge, and f is the rf frequency, respectively. For the application of quantized current in the future current metrology, it is crucial to achieve robust operation across a sufficiently wide gate voltage range. Here, we report a method to extend the quantized current plateau by screening the electrostatic field. We observe that the nth plateau width abruptly increases when the corresponding plateau crosses a certain voltage value applied to a gate capacitively coupled to the QD system. Our analysis, which is based on the decay-cascade model, reveals that the plateau extension behavior originates from a change of the gate-coupling constant at the particular gate voltage. We propose that the change in the gate-coupling constant occurs when the top of the potential barrier under the gate is lower than the Fermi energy. This results in an accumulation of electrons above the potential barrier and an enhanced screening effect for the gate coupling.