diff --git a/key.go b/key.go
index 3b62bf0d..0b526959 100644
--- a/key.go
+++ b/key.go
@@ -112,10 +112,19 @@ func NewKey(namespace string, setName string, key interface{}) (*Key, Error) {
 // NewKeyWithDigest initializes a key from namespace, optional set name and user key.
 // The server handles record identifiers by digest only.
 func NewKeyWithDigest(namespace string, setName string, key interface{}, digest []byte) (*Key, Error) {
+	var userKey Value = nil
+	if key != nil {
+		userKey = NewValue(key)
+		// make sure the key type is valid
+		if err := verifyKey(userKey); err != nil {
+			return nil, err
+		}
+	}
+
 	newKey := &Key{
 		namespace: namespace,
 		setName:   setName,
-		userKey:   NewValue(key),
+		userKey:   userKey,
 	}
 
 	if err := newKey.SetDigest(digest); err != nil {
diff --git a/key_helper.go b/key_helper.go
index 38ead4ff..ec36b20c 100644
--- a/key_helper.go
+++ b/key_helper.go
@@ -152,3 +152,18 @@ func (vb *keyWriter) writeKey(val Value) Error {
 
 	return newError(types.PARAMETER_ERROR, "Key Generation Error. Value not supported: "+val.String())
 }
+
+func verifyKey(val Value) Error {
+	switch val.(type) {
+	case IntegerValue:
+		return nil
+	case LongValue:
+		return nil
+	case StringValue:
+		return nil
+	case BytesValue:
+		return nil
+	}
+
+	return newError(types.PARAMETER_ERROR, "Key Generation Error. Value not supported: "+val.String())
+}
diff --git a/key_test.go b/key_test.go
index 541e80e5..b752a609 100644
--- a/key_test.go
+++ b/key_test.go
@@ -132,7 +132,10 @@ var _ = gg.Describe("Key Test", func() {
 			gm.Expect(err, nil)
 			gm.Expect(key.Digest()).To(gm.Equal([]byte("01234567890123456789")))
 
-			key, _ = as.NewKeyWithDigest("namespace", "set", []interface{}{}, []byte("01234567890123456789"))
+			key, err = as.NewKeyWithDigest("namespace", "set", []interface{}{}, []byte("01234567890123456789"))
+			gm.Expect(err).To(gm.HaveOccurred())
+
+			key, err = as.NewKeyWithDigest("namespace", "set", nil, []byte("01234567890123456789"))
 			gm.Expect(key.Digest()).To(gm.Equal([]byte("01234567890123456789")))
 		})