1 files changed, 4 insertions, 0 deletions
diff --git a/merge.go b/merge.go
index d7400a2..c31416a 100644
--- a/merge.go
+++ b/merge.go
@@ -60,6 +60,8 @@ func (f *File) MergeCell(sheet, hCell, vCell string) error {
 	if err != nil {
 		return err
 	}
+	ws.Lock()
+	defer ws.Unlock()
 	ref := hCell + ":" + vCell
 	if ws.MergeCells != nil {
 		ws.MergeCells.Cells = append(ws.MergeCells.Cells, &xlsxMergeCell{Ref: ref, rect: rect})
@@ -81,6 +83,8 @@ func (f *File) UnmergeCell(sheet string, hCell, vCell string) error {
 	if err != nil {
 		return err
 	}
+	ws.Lock()
+	defer ws.Unlock()
 	rect1, err := areaRefToCoordinates(hCell + ":" + vCell)
 	if err != nil {
 		return err