The reverberation time or RT60 is an essential acoustic parameter of a room. In many situations, the room impulse response (RIR) is not available and the RT60 must be blindly estimated from a speech or music signal. Current methods often implicitly assume that reverberation dominates direct sound, which restricts their applicability to relatively small rooms or distant sound sources. This paper features two contributions. Firstly, we propose a blind RT60 estimation method that is independent of the room size and the source distance by preprocessing the input signal using a beamformer to cancel direct sound and early echoes. Secondly, we perform the largest experimental evaluation to our knowledge using a set of 342 RIRs. We show that the estimation error is significantly reduced even in the case when reverberation dominates.