diff --git a/index/upside_down/row_merge.go b/index/upside_down/row_merge.go
index fb9d987a..bb0e5e39 100644
--- a/index/upside_down/row_merge.go
+++ b/index/upside_down/row_merge.go
@@ -61,8 +61,9 @@ func (m *upsideDownMerge) FullMerge(key, existingValue []byte, operands [][]byte
 func (m *upsideDownMerge) PartialMerge(key, leftOperand, rightOperand []byte) ([]byte, bool) {
 	left := int64(binary.LittleEndian.Uint64(leftOperand))
 	right := int64(binary.LittleEndian.Uint64(rightOperand))
-	binary.LittleEndian.PutUint64(leftOperand, uint64(left+right))
-	return leftOperand, true
+	rv := make([]byte, 8)
+	binary.LittleEndian.PutUint64(rv, uint64(left+right))
+	return rv, true
 }
 
 func (m *upsideDownMerge) Name() string {
diff --git a/index/upside_down/row_merge_test.go b/index/upside_down/row_merge_test.go
new file mode 100644
index 00000000..eee3f071
--- /dev/null
+++ b/index/upside_down/row_merge_test.go
@@ -0,0 +1,52 @@
+//  Copyright (c) 2014 Couchbase, Inc.
+//  Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+//  except in compliance with the License. You may obtain a copy of the License at
+//    http://www.apache.org/licenses/LICENSE-2.0
+//  Unless required by applicable law or agreed to in writing, software distributed under the
+//  License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+//  either express or implied. See the License for the specific language governing permissions
+//  and limitations under the License.
+
+package upside_down
+
+import (
+	"bytes"
+	"encoding/binary"
+	"testing"
+)
+
+func TestPartialMerge(t *testing.T) {
+
+	tests := []struct {
+		in  [][]byte
+		out uint64
+	}{
+		{
+			in:  [][]byte{dictionaryTermIncr, dictionaryTermIncr, dictionaryTermIncr, dictionaryTermIncr, dictionaryTermIncr},
+			out: 5,
+		},
+	}
+
+	mo := &upsideDownMerge{}
+	for _, test := range tests {
+		curr := test.in[0]
+		for _, next := range test.in[1:] {
+			var ok bool
+			curr, ok = mo.PartialMerge([]byte("key"), curr, next)
+			if !ok {
+				t.Errorf("expected partial merge ok")
+			}
+		}
+		actual := decodeCount(curr)
+		if actual != test.out {
+			t.Errorf("expected %d, got %d", test.out, actual)
+		}
+	}
+
+}
+
+func decodeCount(in []byte) uint64 {
+	buf := bytes.NewBuffer(in)
+	count, _ := binary.ReadUvarint(buf)
+	return count
+}