  The positron-neutrino correlation in the $0^+ \to 0^+ \beta$ decay of
$^{32}$Ar was measured at ISOLDE by analyzing the effect of lepton recoil on
the shape of the narrow proton group following the superallowed decay. Our
result is consistent with the Standard Model prediction. For vanishing Fierz
interference we find $a=0.9989 \pm 0.0052 \pm 0.0036$, which yields improved
constraints on scalar weak interactions.
