One of the simplest models that allows for an electroweak (EW) strong first order phase transition (SFOPT) while having a Higgs with the observed mass of 125 GeV is the singlet extension of the Standard Model (SM). We discuss two different phases of a complex singlet extension of the SM. If the singlet has a zero vacuum expectation value (VEV) the situation is exactly the same as in the SM with no SFOPT. However, when the singlet acquires a VEV, a SFOPT is possible, giving rise to detectable gravitational waves (GWs) by LISA. The model also provides a dark matter candidate. We have studied the impact of the SM particle masses on the strength of the GWs spectrum. It turns out that the variation of the Higgs boson and top quark masses within one standard deviation of the experimentally measured value has a noticeable impact on GWs detectability prospects.