gogost.go                |  2 +-
 gost3410/vko.go          |  6 +++---
 gost3410/vko2001_test.go | 21 +++++++++++++++++++++
 news.texi                |  5 +++++

diff --git a/gogost.go b/gogost.go
index 99c5e211ca598800a499325ca8dcd4ff91f450e9722cd940318dcc1a3bfc4723..d882a31bb990a14bbda87a479b91eccbc70cff11c74cd64b1c57b9ed5bdbc70f 100644
--- a/gogost.go
+++ b/gogost.go
@@ -1,4 +1,4 @@
 // Pure Go GOST cryptographic functions library.
 package gogost
 
-const Version = "5.0.2"
+const Version = "5.1.0"
diff --git a/gost3410/vko.go b/gost3410/vko.go
index ea5571658220fe121d46618df189d6f21ce40affb40309adfda76f257e1dc054..e64e7dcb8ece56098ff1e3db86f4f11b91b4fb6fb6b7428cd24642f0e5c24e6b 100644
--- a/gost3410/vko.go
+++ b/gost3410/vko.go
@@ -24,9 +24,9 @@ 	keyX, keyY, err := prv.C.Exp(prv.Key, pub.X, pub.Y)
 	if err != nil {
 		return nil, err
 	}
-	ukm = ukm.Mul(ukm, prv.C.Co)
-	if ukm.Cmp(bigInt1) != 0 {
-		keyX, keyY, err = prv.C.Exp(ukm, keyX, keyY)
+	u := big.NewInt(0).Set(ukm).Mul(ukm, prv.C.Co)
+	if u.Cmp(bigInt1) != 0 {
+		keyX, keyY, err = prv.C.Exp(u, keyX, keyY)
 		if err != nil {
 			return nil, err
 		}
diff --git a/gost3410/vko2001_test.go b/gost3410/vko2001_test.go
index f8f8456c8ac16b2d29251630b343fb8577b925fbc5ef05a4e12d88044887a53a..b44db1788f387bb5f6abff19ab9645ac3a3c86c9bb4fb8d521eedfb0287d0d35 100644
--- a/gost3410/vko2001_test.go
+++ b/gost3410/vko2001_test.go
@@ -18,6 +18,7 @@
 import (
 	"bytes"
 	"encoding/hex"
+	"math/big"
 	"testing"
 	"testing/quick"
 )
@@ -39,6 +40,26 @@ 	if bytes.Compare(kek1, kek2) != 0 {
 		t.FailNow()
 	}
 	if bytes.Compare(kek1, kek) != 0 {
+		t.FailNow()
+	}
+}
+
+func TestVKOUKMAltering(t *testing.T) {
+	c := CurveIdtc26gost34102012256paramSetA()
+	ukm := big.NewInt(1)
+	prv, err := NewPrivateKey(c, bytes.Repeat([]byte{0x12}, 32))
+	if err != nil {
+		panic(err)
+	}
+	pub, err := prv.PublicKey()
+	if err != nil {
+		panic(err)
+	}
+	_, err = prv.KEK(pub, ukm)
+	if err != nil {
+		panic(err)
+	}
+	if ukm.Cmp(big.NewInt(1)) != 0 {
 		t.FailNow()
 	}
 }
diff --git a/news.texi b/news.texi
index 89b65b45993bf0ee72c8a2204c7c41feffece0b34844127e15eec24029c2221a..b8bb7af3d17b726149f845d31caf992f2c9bcedd974dcca13b0cfd7bfdb2cbf6 100644
--- a/news.texi
+++ b/news.texi
@@ -3,6 +3,11 @@ @unnumbered News
 
 @table @strong
 
+@anchor{Release 5.1.0}
+@item 5.1.0
+    @code{gost3410/KEK*} functions do not alter @code{ukm} argument.
+    It is safe to reuse now.
+
 @anchor{Release 5.0.0}
 @item 5.0.0
     Backward incompatible remove of excess misleading @code{gost3410.Mode}