diff --git a/bump.go b/bump.go
index 4b0274b..6e8093b 100644
--- a/bump.go
+++ b/bump.go
@@ -30,6 +30,9 @@ type leaf struct {
 
 // NewBUMPFromBytes creates a new BUMP from a byte slice.
 func NewBUMPFromBytes(bytes []byte) (*BUMP, error) {
+	if len(bytes) < 37 {
+		return nil, errors.New("BUMP bytes do not contain enough data to be valid")
+	}
 	bump := &BUMP{}
 
 	// first bytes are the block height.
@@ -50,6 +53,9 @@ func NewBUMPFromBytes(bytes []byte) (*BUMP, error) {
 		n, size := bt.NewVarIntFromBytes(bytes[skip:])
 		skip += size
 		nLeavesAtThisHeight := uint64(n)
+		if nLeavesAtThisHeight == 0 {
+			return nil, errors.New("There are no leaves at height: " + fmt.Sprint(lv) + " which makes this invalid")
+		}
 		bump.Path[lv] = make([]leaf, nLeavesAtThisHeight)
 		for lf := uint64(0); lf < nLeavesAtThisHeight; lf++ {
 			// For each leaf we parse the offset, hash, txid and duplicate.
@@ -65,6 +71,9 @@ func NewBUMPFromBytes(bytes []byte) (*BUMP, error) {
 			if dup {
 				l.Duplicate = &dup
 			} else {
+				if len(bytes) < skip+32 {
+					return nil, errors.New("BUMP bytes do not contain enough data to be valid")
+				}
 				h := StringFromBytesReverse(bytes[skip : skip+32])
 				l.Hash = &h
 				skip += 32
@@ -142,8 +151,11 @@ func (bump *BUMP) String() (string, error) {
 
 // CalculateRootGivenTxid calculates the root of the Merkle tree given a txid.
 func (bump *BUMP) CalculateRootGivenTxid(txid string) (string, error) {
-	if len(bump.Path) < 2 {
-		return txid, nil
+	if len(bump.Path) == 1 {
+		// if there is only one txid in the block then the root is the txid.
+		if len(bump.Path[0]) == 1 {
+			return txid, nil
+		}
 	}
 	// Find the index of the txid at the lowest level of the Merkle tree
 	var index uint64
@@ -233,7 +245,7 @@ func NewBUMPFromMerkleTreeAndIndex(blockHeight uint64, merkleTree []*chainhash.H
 				} else {
 					sh := hash.String()
 					thisLeaf.Hash = &sh
-					if height == 0 {
+					if height == 0 && txIndex == o {
 						thisLeaf.Txid = &t
 					}
 				}
diff --git a/bump_test.go b/bump_test.go
index 9687568..946ca6a 100644
--- a/bump_test.go
+++ b/bump_test.go
@@ -20,6 +20,11 @@ const (
 	testnetHexExample  = `0202ac5abbdc202bd6d50260825dd5465bd0798b052b2115c7abed277a41e403b21d0a61f6e257da3871657d324a31a449aa58a83b61967f1f2192eca71b3c21f68f`
 	testnetRootExample = `e4bbc8329d950749cb844ba2dac1e09bfc418d5c96d03fb688eff95bb90965b8`
 	testnetTxidExample = `8d15f64f8a35e94eb3cdbc07d9bc28952fdbdd13315fe3a94b393e635a9307aa`
+
+	twoTxExample = `fd0d020102000209d1fab394d14fc4d5819dffe7af320744b51469569fde7bd76c57c917d91ce10102b98551d22cd578c430374bde629322f72b72c9f64f5425ac307b679cfacd4525`
+	twoTxid      = `2545cdfa9c677b30ac25544ff6c9722bf7229362de4b3730c478d52cd25185b9`
+
+	oneTxidHeightOne = `0101010102912f77eefdd311e24f96850ed8e701381fc4943327f9cf73f9c4dec0d93a056d`
 )
 
 var testnetBlockExample = []string{
@@ -116,3 +121,34 @@ func TestTestnetCalculateRootGivenTxid(t *testing.T) {
 		require.Equal(t, testnetRootExample, root)
 	}
 }
+
+func TestTwoTxsInBlock(t *testing.T) {
+	bump, err := NewBUMPFromStr(twoTxExample)
+	require.NoError(t, err)
+
+	_, err = bump.CalculateRootGivenTxid(twoTxid)
+	require.NoError(t, err)
+}
+
+func TestOneTxidHeightOne(t *testing.T) {
+	bump, err := NewBUMPFromStr(oneTxidHeightOne)
+	require.NoError(t, err)
+
+	_, err = bump.CalculateRootGivenTxid("6d053ad9c0dec4f973cff9273394c41f3801e7d80e85964fe211d3fdee772f91")
+	require.NoError(t, err)
+}
+
+func TestEmptyBytes(t *testing.T) {
+	_, err := NewBUMPFromStr("")
+	require.Error(t, err)
+}
+
+func TestTooFewBytes(t *testing.T) {
+	_, err := NewBUMPFromStr("01010101026d053ad9c0dec4f973cff9273394c41f3801e7d80e85964fe211d3fdee772f")
+	require.Error(t, err)
+}
+
+func TestNotEnoughLeavesInHeight(t *testing.T) {
+	_, err := NewBUMPFromStr("01020101026d053ad9c0dec4f973cff9273394c41f3801e7d80e85964fe211d3fdee772f9100")
+	require.Error(t, err)
+}