diff --git a/src/pkg/syscall/ztypes_windows_386.go b/src/pkg/syscall/ztypes_windows_386.go
index 0780d190ac..c157a6525c 100644
--- a/src/pkg/syscall/ztypes_windows_386.go
+++ b/src/pkg/syscall/ztypes_windows_386.go
@@ -308,7 +308,7 @@ const (
 	SO_UPDATE_ACCEPT_CONTEXT = 0x700b
 
 	IPPROTO_IPV6 = 0x29
-	IPV6_V6ONLY  = 0x1a
+	IPV6_V6ONLY  = 0x1b
 
 	SOMAXCONN = 5