diff --git a/ipv4/helper.go b/ipv4/helper.go
index a4457d60..25e75680 100644
--- a/ipv4/helper.go
+++ b/ipv4/helper.go
@@ -24,14 +24,15 @@ var (
 	errNoSuchMulticastInterface = errors.New("no such multicast interface")
 	errNotImplemented           = errors.New("not implemented on " + runtime.GOOS + "/" + runtime.GOARCH)
 
-	// See http://www.freebsd.org/doc/en/books/porters-handbook/freebsd-versions.html.
+	// See https://www.freebsd.org/doc/en/books/porters-handbook/versions.html.
 	freebsdVersion  uint32
 	compatFreeBSD32 bool // 386 emulation on amd64
 )
 
 // See golang.org/issue/30899.
 func adjustFreeBSD32(m *socket.Message) {
-	if freebsdVersion >= 1103000 {
+	// FreeBSD 12.0-RELEASE is affected by https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236737
+	if freebsdVersion >= 1200086 && freebsdVersion < 1201000 {
 		l := (m.NN + 4 - 1) &^ (4 - 1)
 		if m.NN < l && l <= len(m.OOB) {
 			m.NN = l