diff --git a/hash/hash.go b/hash/hash.go
index 4c005e976..73349d89a 100644
--- a/hash/hash.go
+++ b/hash/hash.go
@@ -19,6 +19,13 @@ var DefaultHash = sha256.New
 // size is a default size for hashing algorithm.
 var size = DefaultHash().Size()
 
+func checkLen(data []byte) error {
+	if len(data) != size {
+		return fmt.Errorf("hash: invalid length")
+	}
+	return nil
+}
+
 // Digest represents the partial evaluation of a checksum.
 type Digest struct {
 	hash.Hash
@@ -67,11 +74,9 @@ func Random() (Hash, error) {
 	if err != nil {
 		return nil, fmt.Errorf("hash generate random error: %s", err)
 	}
-
 	if n != size {
 		return nil, fmt.Errorf("hash generate random error: invalid hash length")
 	}
-
 	return hash, nil
 }
 
@@ -82,8 +87,8 @@ func Decode(h string) (Hash, error) {
 	if err != nil {
 		return nil, fmt.Errorf("hash: %s", err)
 	}
-	if len(hash) != size {
-		return nil, fmt.Errorf("hash: invalid length string")
+	if err := checkLen(hash); err != nil {
+		return nil, err
 	}
 	return Hash(hash), nil
 }
@@ -105,16 +110,19 @@ func (h Hash) Equal(h1 Hash) bool {
 
 // Marshal marshals hash into slice of bytes. It's used by protobuf.
 func (h Hash) Marshal() ([]byte, error) {
-	return h, nil
+	return h, checkLen(h)
 }
 
 // MarshalTo marshals hash into slice of bytes. It's used by protobuf.
 func (h Hash) MarshalTo(data []byte) (int, error) {
-	return copy(data, h), nil
+	return copy(data, h), checkLen(h)
 }
 
 // Unmarshal unmarshals slice of bytes into hash. It's used by protobuf.
 func (h *Hash) Unmarshal(data []byte) error {
+	if err := checkLen(data); err != nil {
+		return err
+	}
 	*h = make([]byte, len(data))
 	copy(*h, data)
 	return nil
@@ -122,10 +130,7 @@ func (h *Hash) Unmarshal(data []byte) error {
 
 // Size retruns size of hash. It's used by protobuf.
 func (h Hash) Size() int {
-	if len(h) == 0 {
-		return 0
-	}
-	return size
+	return len(h)
 }
 
 // MarshalJSON mashals hash into encoded json string.
@@ -139,16 +144,13 @@ func (h *Hash) UnmarshalJSON(data []byte) error {
 	if err := json.Unmarshal(data, &str); err != nil {
 		return err
 	}
-
 	if str == "" {
 		return nil
 	}
-
 	h1, err := base58.Decode(str)
 	if err != nil {
 		return err
 	}
-
 	*h = Hash(h1)
 	return nil
 }
diff --git a/hash/hash_test.go b/hash/hash_test.go
index db0c786ab..6607d9237 100644
--- a/hash/hash_test.go
+++ b/hash/hash_test.go
@@ -60,7 +60,7 @@ func TestDecode(t *testing.T) {
 	assert.Equal(t, "hash: invalid base58 digit ('0')", err.Error())
 
 	_, err = Decode("1")
-	assert.Equal(t, "hash: invalid length string", err.Error())
+	assert.Equal(t, "hash: invalid length", err.Error())
 }
 
 func TestIsZero(t *testing.T) {
@@ -79,6 +79,7 @@ func TestEqual(t *testing.T) {
 func TestSize(t *testing.T) {
 	assert.Equal(t, 0, Hash(nil).Size())
 	assert.Equal(t, size, zero.Size())
+	assert.Equal(t, 5, Hash([]byte("hello")).Size())
 }
 
 func TestMarshalJSON(t *testing.T) {
@@ -101,3 +102,19 @@ func TestUnmarshal(t *testing.T) {
 	// test if two slises do not share the same address
 	assert.True(t, &hash[cap(hash)-1] != &data[cap(data)-1])
 }
+
+func TestWrongLength(t *testing.T) {
+	var h Hash
+	wrongLenByte := []byte("hello")
+	t.Run("Marshal", func(t *testing.T) {
+		_, err := Hash(wrongLenByte).Marshal()
+		require.EqualError(t, err, "hash: invalid length")
+	})
+	t.Run("MarshalTo", func(t *testing.T) {
+		_, err := h.MarshalTo(wrongLenByte)
+		require.EqualError(t, err, "hash: invalid length")
+	})
+	t.Run("Unmarshal", func(t *testing.T) {
+		require.EqualError(t, h.Unmarshal(wrongLenByte), "hash: invalid length")
+	})
+}