diff --git a/wgengine/filter/match.go b/wgengine/filter/match.go
index 572595c7b..651c7f83d 100644
--- a/wgengine/filter/match.go
+++ b/wgengine/filter/match.go
@@ -47,8 +47,7 @@ var NetAny = Net{0, 0}
 var NetNone = Net{^IP(0), ^IP(0)}
 
 func Netmask(bits int) IP {
-	var b uint32
-	b = ^uint32((1 << (32 - bits)) - 1)
+	b := ^uint32((1 << (32 - bits)) - 1)
 	return IP(b)
 }