diff --git a/lib/spreadsheet/excel/writer/worksheet.rb b/lib/spreadsheet/excel/writer/worksheet.rb
index 08212a3..f626ef2 100644
--- a/lib/spreadsheet/excel/writer/worksheet.rb
+++ b/lib/spreadsheet/excel/writer/worksheet.rb
@@ -158,7 +158,7 @@ def write_calccount
     write_op 0x000c, [count].pack('v')
   end
   def write_cell type, row, idx, *args
-    xf_idx = @workbook.xf_index @worksheet.workbook, row.formats[idx]
+    xf_idx = @workbook.xf_index @worksheet.workbook, row.format(idx)
     data = [
       row.idx, # Index to row
       idx,     # Index to column
@@ -358,7 +358,7 @@ def write_eof
   # Write a cell with a Formula. May write an additional String record depending
   # on the stored result of the Formula.
   def write_formula row, idx
-    xf_idx = @workbook.xf_index @worksheet.workbook, row.formats[idx]
+    xf_idx = @workbook.xf_index @worksheet.workbook, row.format(idx)
     cell = row[idx]
     data1 = [
       row.idx,      # Index to row
@@ -562,7 +562,7 @@ def write_mulblank row, idx, multiples
     ]
     # List of nc=lc-fc+1 16-bit indexes to XF records (➜ 6.115)
     multiples.each_with_index do |blank, cell_idx|
-      xf_idx = @workbook.xf_index @worksheet.workbook, row.formats[idx + cell_idx]
+      xf_idx = @workbook.xf_index @worksheet.workbook, row.format(idx + cell_idx)
       data.push xf_idx
     end
     # Index to last column (lc)
diff --git a/test/integration.rb b/test/integration.rb
index b506650..3a51cb5 100644
--- a/test/integration.rb
+++ b/test/integration.rb
@@ -580,7 +580,7 @@ def test_change_cell
       sheet = book.worksheet 0
       assert_equal 11, sheet.row_count
       assert_equal 12, sheet.column_count
-      useds = [0,0,0,0,0,0,0,1,0,0,11]
+      useds = [0,0,0,0,0,0,0,0,0,0,0]
       unuseds = [2,2,1,1,1,2,1,11,1,2,12]
       sheet.each do |row|
         assert_equal useds.shift, row.first_used
@@ -689,7 +689,7 @@ def test_change_cell__complete_sst_rewrite
       sheet = book.worksheet 0
       assert_equal 11, sheet.row_count
       assert_equal 12, sheet.column_count
-      useds = [0,0,0,0,0,0,0,1,0,0,11]
+      useds = [0,0,0,0,0,0,0,0,0,0,0]
       unuseds = [2,2,1,1,1,2,1,11,1,2,12]
       sheet.each do |row|
         assert_equal useds.shift, row.first_used