diff --git a/ipv4/header.go b/ipv4/header.go
index b22336c..0cf9c98 100644
--- a/ipv4/header.go
+++ b/ipv4/header.go
@@ -5,7 +5,6 @@
 package ipv4
 
 import (
-	"errors"
 	"fmt"
 	"net"
 	"runtime"
@@ -13,14 +12,6 @@
 	"unsafe"
 )
 
-var (
-	errMissingAddress  = errors.New("missing address")
-	errMissingHeader   = errors.New("missing header")
-	errHeaderTooShort  = errors.New("header too short")
-	errBufferTooShort  = errors.New("buffer too short")
-	errInvalidConnType = errors.New("invalid conn type")
-)
-
 const (
 	Version      = 4  // protocol version
 	HeaderLen    = 20 // header length without extension headers
diff --git a/ipv4/helper.go b/ipv4/helper.go
index 20c2d24..8a7ee90 100644
--- a/ipv4/helper.go
+++ b/ipv4/helper.go
@@ -10,6 +10,11 @@
 )
 
 var (
+	errMissingAddress           = errors.New("missing address")
+	errMissingHeader            = errors.New("missing header")
+	errHeaderTooShort           = errors.New("header too short")
+	errBufferTooShort           = errors.New("buffer too short")
+	errInvalidConnType          = errors.New("invalid conn type")
 	errOpNoSupport              = errors.New("operation not supported")
 	errNoSuchInterface          = errors.New("no such interface")
 	errNoSuchMulticastInterface = errors.New("no such multicast interface")