diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index 31bb2aefa..38f8103c6 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -431,7 +431,8 @@ func (bc *Blockchain) storeBlock(block *block.Block) error {
 		}
 
 		// Process TX inputs that are grouped by previous hash.
-		for prevHash, inputs := range tx.GroupInputsByPrevHash() {
+		for _, inputs := range transaction.GroupInputsByPrevHash(tx.Inputs) {
+			prevHash := inputs[0].PrevHash
 			prevTX, prevTXHeight, err := bc.dao.GetTransaction(prevHash)
 			if err != nil {
 				return fmt.Errorf("could not find previous TX: %s", prevHash)
@@ -1016,7 +1017,8 @@ func (bc *Blockchain) GetConfig() config.ProtocolConfiguration {
 func (bc *Blockchain) References(t *transaction.Transaction) map[transaction.Input]*transaction.Output {
 	references := make(map[transaction.Input]*transaction.Output)
 
-	for prevHash, inputs := range t.GroupInputsByPrevHash() {
+	for _, inputs := range transaction.GroupInputsByPrevHash(t.Inputs) {
+		prevHash := inputs[0].PrevHash
 		tx, _, err := bc.dao.GetTransaction(prevHash)
 		if err != nil {
 			return nil
diff --git a/pkg/core/dao.go b/pkg/core/dao.go
index c5c2c1a76..cba1d59c5 100644
--- a/pkg/core/dao.go
+++ b/pkg/core/dao.go
@@ -547,7 +547,8 @@ func (dao *dao) IsDoubleSpend(tx *transaction.Transaction) bool {
 	if len(tx.Inputs) == 0 {
 		return false
 	}
-	for prevHash, inputs := range tx.GroupInputsByPrevHash() {
+	for _, inputs := range transaction.GroupInputsByPrevHash(tx.Inputs) {
+		prevHash := inputs[0].PrevHash
 		unspent, err := dao.GetUnspentCoinState(prevHash)
 		if err != nil {
 			return false
diff --git a/pkg/core/transaction/input.go b/pkg/core/transaction/input.go
index da390cfe5..b1e6b7694 100644
--- a/pkg/core/transaction/input.go
+++ b/pkg/core/transaction/input.go
@@ -1,6 +1,8 @@
 package transaction
 
 import (
+	"sort"
+
 	"github.com/CityOfZion/neo-go/pkg/io"
 	"github.com/CityOfZion/neo-go/pkg/util"
 )
@@ -25,3 +27,34 @@ func (in *Input) EncodeBinary(bw *io.BinWriter) {
 	bw.WriteBytes(in.PrevHash[:])
 	bw.WriteU16LE(in.PrevIndex)
 }
+
+// GroupInputsByPrevHash groups all TX inputs by their previous hash into
+// several slices (which actually are subslices of one new slice with pointers).
+// Each of these slices contains at least one element.
+func GroupInputsByPrevHash(ins []Input) [][]*Input {
+	if len(ins) == 0 {
+		return nil
+	}
+
+	ptrs := make([]*Input, len(ins))
+	for i := range ins {
+		ptrs[i] = &ins[i]
+	}
+	sort.Slice(ptrs, func(i, j int) bool {
+		return ptrs[i].PrevHash.CompareTo(ptrs[j].PrevHash) < 0
+	})
+
+	var first int
+	res := make([][]*Input, 0)
+	currentHash := ptrs[0].PrevHash
+
+	for i := range ptrs {
+		if !currentHash.Equals(ptrs[i].PrevHash) {
+			res = append(res, ptrs[first:i])
+			first = i
+			currentHash = ptrs[i].PrevHash
+		}
+	}
+	res = append(res, ptrs[first:])
+	return res
+}
diff --git a/pkg/core/transaction/input_test.go b/pkg/core/transaction/input_test.go
new file mode 100644
index 000000000..2b3f595ef
--- /dev/null
+++ b/pkg/core/transaction/input_test.go
@@ -0,0 +1,75 @@
+package transaction
+
+import (
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/util"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGroupInputsByPrevHash0(t *testing.T) {
+	inputs := make([]Input, 0)
+	res := GroupInputsByPrevHash(inputs)
+	require.Equal(t, 0, len(res))
+}
+
+func TestGroupInputsByPrevHash1(t *testing.T) {
+	inputs := make([]Input, 0)
+	hash, err := util.Uint256DecodeStringLE("46168f963d6d8168a870405f66cc9e13a235791013b8ee2f90cc20a8293bd1af")
+	require.NoError(t, err)
+	inputs = append(inputs, Input{PrevHash: hash, PrevIndex: 42})
+	res := GroupInputsByPrevHash(inputs)
+	require.Equal(t, 1, len(res))
+	require.Equal(t, 1, len(res[0]))
+	assert.Equal(t, hash, res[0][0].PrevHash)
+	assert.Equal(t, uint16(42), res[0][0].PrevIndex)
+}
+
+func TestGroupInputsByPrevHashMany(t *testing.T) {
+	hash1, err := util.Uint256DecodeStringBE("a83ba6ede918a501558d3170a124324aedc89909e64c4ff2c6f863094f980b25")
+	require.NoError(t, err)
+	hash2, err := util.Uint256DecodeStringBE("629397158f852e838077bb2715b13a2e29b0a51c2157e5466321b70ed7904ce9")
+	require.NoError(t, err)
+	hash3, err := util.Uint256DecodeStringBE("caa41245c3e48ddc13dabe989ba8fbc59418e9228fef9efb62855b0b17d7448b")
+	require.NoError(t, err)
+	inputs := make([]Input, 0)
+	for i := 0; i < 10; i++ {
+		inputs = append(inputs, Input{PrevHash: hash1, PrevIndex: uint16(i)})
+		inputs = append(inputs, Input{PrevHash: hash2, PrevIndex: uint16(i)})
+		inputs = append(inputs, Input{PrevHash: hash3, PrevIndex: uint16(i)})
+	}
+	for i := 15; i < 20; i++ {
+		inputs = append(inputs, Input{PrevHash: hash3, PrevIndex: uint16(i)})
+	}
+	for i := 10; i < 15; i++ {
+		inputs = append(inputs, Input{PrevHash: hash2, PrevIndex: uint16(i)})
+		inputs = append(inputs, Input{PrevHash: hash3, PrevIndex: uint16(i)})
+	}
+	seen := make(map[uint16]bool)
+	res := GroupInputsByPrevHash(inputs)
+	require.Equal(t, 3, len(res))
+	assert.Equal(t, hash2, res[0][0].PrevHash)
+	assert.Equal(t, 15, len(res[0]))
+	for i := range res[0] {
+		assert.Equal(t, res[0][i].PrevHash, res[0][0].PrevHash)
+		assert.Equal(t, false, seen[res[0][i].PrevIndex])
+		seen[res[0][i].PrevIndex] = true
+	}
+	seen = make(map[uint16]bool)
+	assert.Equal(t, hash1, res[1][0].PrevHash)
+	assert.Equal(t, 10, len(res[1]))
+	for i := range res[1] {
+		assert.Equal(t, res[1][i].PrevHash, res[1][0].PrevHash)
+		assert.Equal(t, false, seen[res[1][i].PrevIndex])
+		seen[res[1][i].PrevIndex] = true
+	}
+	seen = make(map[uint16]bool)
+	assert.Equal(t, hash3, res[2][0].PrevHash)
+	assert.Equal(t, 20, len(res[2]))
+	for i := range res[2] {
+		assert.Equal(t, res[2][i].PrevHash, res[2][0].PrevHash)
+		assert.Equal(t, false, seen[res[2][i].PrevIndex])
+		seen[res[2][i].PrevIndex] = true
+	}
+}
diff --git a/pkg/core/transaction/transaction.go b/pkg/core/transaction/transaction.go
index 46c0bee77..cdabfa3c0 100644
--- a/pkg/core/transaction/transaction.go
+++ b/pkg/core/transaction/transaction.go
@@ -187,16 +187,6 @@ func (t *Transaction) createHash() error {
 	return nil
 }
 
-// GroupInputsByPrevHash groups all TX inputs by their previous hash.
-func (t *Transaction) GroupInputsByPrevHash() map[util.Uint256][]*Input {
-	m := make(map[util.Uint256][]*Input)
-	for i := range t.Inputs {
-		hash := t.Inputs[i].PrevHash
-		m[hash] = append(m[hash], &t.Inputs[i])
-	}
-	return m
-}
-
 // GroupOutputByAssetID groups all TX outputs by their assetID.
 func (t Transaction) GroupOutputByAssetID() map[util.Uint256][]*Output {
 	m := make(map[util.Uint256][]*Output)