diff --git a/.gitignore b/.gitignore
index 685d2bfdc54ebc5542a84f5140677106bcf331bb..ce92812619c3540342f387fafddd5c03150303f0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,10 @@
 ~$*.xlsx
 test/Test*.xlsx
 test/Test*.xlsm
+# generated files
+test/BadEncrypt.xlsx
+test/BadWorkbook.SaveAsEmptyStruct.xlsx
+test/*.png
 *.out
 *.test
 .idea
diff --git a/cell.go b/cell.go
index 1edfd24b251cb4e4bdff9dc7f9af11e6490b11f9..22adefd4548026e8198f7610ee36ac483a60ad79 100644
--- a/cell.go
+++ b/cell.go
@@ -762,10 +762,15 @@ func (f *File) formattedValue(s int, v string) string {
 		return v
 	}
 	styleSheet := f.stylesReader()
+
 	if s >= len(styleSheet.CellXfs.Xf) {
 		return v
 	}
-	numFmtID := *styleSheet.CellXfs.Xf[s].NumFmtID
+	var numFmtID int
+	if styleSheet.CellXfs.Xf[s].NumFmtID != nil {
+		numFmtID = *styleSheet.CellXfs.Xf[s].NumFmtID
+	}
+
 	ok := builtInNumFmtFunc[numFmtID]
 	if ok != nil {
 		return ok(v, builtInNumFmt[numFmtID])
diff --git a/cell_test.go b/cell_test.go
index c934876edb1eb0b2c2b0bbd81a60ec43450a8980..8d3f77482d06717edf39a846a3c926facecf17bf 100644
--- a/cell_test.go
+++ b/cell_test.go
@@ -301,7 +301,7 @@ func TestSetCellRichText(t *testing.T) {
 	assert.EqualError(t, f.SetCellRichText("Sheet1", "A", richTextRun), `cannot convert cell "A" to coordinates: invalid cell name "A"`)
 }
 
-func TestFormattedValue(t *testing.T) {
+func TestFormattedValue2(t *testing.T) {
 	f := NewFile()
 	v := f.formattedValue(0, "43528")
 	assert.Equal(t, "43528", v)
@@ -320,12 +320,24 @@ func TestFormattedValue(t *testing.T) {
 	assert.Equal(t, "03/04/2019", v)
 
 	// formatted value with no built-in number format ID
-	assert.NoError(t, err)
-	f.Styles.NumFmts = nil
 	numFmtID := 5
 	f.Styles.CellXfs.Xf = append(f.Styles.CellXfs.Xf, xlsxXf{
 		NumFmtID: &numFmtID,
 	})
+	v = f.formattedValue(2, "43528")
+	assert.Equal(t, "43528", v)
+
+	// formatted value with invalid number format ID
+	f.Styles.CellXfs.Xf = append(f.Styles.CellXfs.Xf, xlsxXf{
+		NumFmtID: nil,
+	})
+	v = f.formattedValue(3, "43528")
+
+	// formatted value with empty number format
+	f.Styles.NumFmts = nil
+	f.Styles.CellXfs.Xf = append(f.Styles.CellXfs.Xf, xlsxXf{
+		NumFmtID: &numFmtID,
+	})
 	v = f.formattedValue(1, "43528")
 	assert.Equal(t, "43528", v)
 }