diff --git a/types/tx.go b/types/tx.go
index e7c454f0..bcff2633 100644
--- a/types/tx.go
+++ b/types/tx.go
@@ -36,6 +36,11 @@ func (txs Txs) Hash() []byte {
 
 // Index returns the index of this transaction in the list, or -1 if not found
 func (txs Txs) Index(tx Tx) int {
+	for i := range txs {
+		if bytes.Equal(txs[i], tx) {
+			return i
+		}
+	}
 	return -1
 }
 
diff --git a/types/tx_test.go b/types/tx_test.go
index 3be66963..aa20f744 100644
--- a/types/tx_test.go
+++ b/types/tx_test.go
@@ -23,6 +23,20 @@ func randInt(low, high int) int {
 	return low + off
 }
 
+func TestTxIndex(t *testing.T) {
+	assert := assert.New(t)
+	for i := 0; i < 20; i++ {
+		txs := makeTxs(15, 60)
+		for j := 0; j < len(txs); j++ {
+			tx := txs[j]
+			idx := txs.Index(tx)
+			assert.Equal(j, idx)
+		}
+		assert.Equal(-1, txs.Index(nil))
+		assert.Equal(-1, txs.Index(Tx("foodnwkf")))
+	}
+}
+
 func TestValidTxProof(t *testing.T) {
 	assert := assert.New(t)
 	cases := []struct {