The observed dark matter abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during inflation and has sufficiently strong self-coupling. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. The self-interaction of the field suppresses its fluctuations on large scales and, therefore, avoids isocurvature constraints. The scenario does not require any fine-tuning of parameters. In the simplest case of a single real scalar field, the mass of the dark matter particle is in the range
1
 
 
GeV
≲
m
≲
10
8
 
 
GeV
, depending on the scale of inflation, and the lower bound for the quartic self-coupling is
λ
≳
0.45
.