How to successfully execute a coup? The literature has mostly focused on identifying the conditions under which coups happen and achieve durable regime change. In this paper, I show that the actions of conspirators during a coup matter and highlight the strategic importance of control over means of communications to deter the coordination of anti-coup challengers. Based on Louis-Napoleon Bonaparte’s coup in December 1851 that caused the breakdown of the Second Republic (1848-1851), I examine the effect of quasi-random interruptions in telegraphic communications between coup-plotters in Paris and bureaucrats (prefects) in the rest of France on the local size of anti-coup insurgency. I collected and digitized the full record of all time-stamped telegraphic dispatches exchanged during the coup (+4000 dispatches). This rich dataset allows an hour-by-hour examination of the effects of uncertainty on mobilization. I demonstrate that when the conspirators controlled information flows, they could prevent the rise of pro-democracy dissent and clear the path towards autocracy. By contrast, when communications with Paris were interrupted, local bureaucrats remained uncertain and stayed passive while mass unrest grew jeopardizing the success of the coup. At a broader level, the study highlights that control over communication infrastructure is a key instrument of state power.