This paper proposes a fast unambiguous acquisition technique for binary-offset-carrier (BOC)-modulated signals. We remove the ambiguities (side peaks) of the BOC autocorrelation function (ACF), exploiting a reduced-complexity (real and symmetric) filter composed of only seven nonzero samples. The proposed scheme is applicable to both generic sine- and cosine-phased BOC signals. Theoretical and simulation results show that the proposed method removes the ambiguities in the acquisition problem without requiring an auxiliary signal in the receiver.