diff --git a/crypto/crypto.go b/crypto/crypto.go
index 035d304a8..258348e96 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -48,7 +48,6 @@ type SigningKey struct {
 	K [16]byte `json:"k"` // for AES128
 	R [16]byte `json:"r"` // for Poly1305
 }
-type iv [ivSize]byte
 
 // mask for key, (cf. http://cr.yp.to/mac/poly1305-20050329.pdf)
 var poly1305KeyMask = [16]byte{
@@ -160,12 +159,13 @@ func NewKey() (k *Key) {
 	return k
 }
 
-func newIV() (iv iv) {
-	n, err := rand.Read(iv[:])
+func newIV() []byte {
+	iv := make([]byte, ivSize)
+	n, err := rand.Read(iv)
 	if n != ivSize || err != nil {
 		panic("unable to read enough random bytes for iv")
 	}
-	return
+	return iv
 }
 
 type jsonMACKey struct {
diff --git a/crypto/writer.go b/crypto/writer.go
index 5ac51ee8d..e56e542aa 100644
--- a/crypto/writer.go
+++ b/crypto/writer.go
@@ -10,7 +10,7 @@ import (
 )
 
 type encryptWriter struct {
-	iv      iv
+	iv      []byte
 	wroteIV bool
 	data    *bytes.Buffer
 	key     *Key