diff --git a/src/pkg/net/ipsock.go b/src/pkg/net/ipsock.go
index d1fcb4852f..9d48e8c103 100644
--- a/src/pkg/net/ipsock.go
+++ b/src/pkg/net/ipsock.go
@@ -8,7 +8,12 @@ package net
 
 import "time"
 
-var supportsIPv6, supportsIPv4map = probeIPv6Stack()
+var supportsIPv6, supportsIPv4map bool
+
+func init() {
+	sysInit()
+	supportsIPv6, supportsIPv4map = probeIPv6Stack()
+}
 
 func firstFavoriteAddr(filter func(IP) IP, addrs []string) (addr IP) {
 	if filter == nil {