Answering a question posed by Caro, Hansberg, Lauri, and Zarb, we show that for every positive integer $n$ and every function $σ\colon E(K_{4n})\to\{-1,1\}$ with $σ\left(E(K_{4n})\right)=0$, there is a perfect matching $M$ in $K_{4n}$ with $σ(M)=0$. Strengthening a result of Caro and Yuster, we show that for every positive integer $n$ and every function $σ\colon E(K_{4n})\to\{-1,1\}$ with $\left|σ\left(E(K_{4n})\right)\right|<n^2+11n+2,$ there is a perfect matching $M$ in $K_{4n}$ with $|σ(M)|\leq 2$. Both these results are best possible.