diff --git a/lib/fast_excel.rb b/lib/fast_excel.rb
index fcc0f49..6ba6b40 100644
--- a/lib/fast_excel.rb
+++ b/lib/fast_excel.rb
@@ -541,7 +541,7 @@ def enable_filters!(start_col: 0, end_col:)
 
     def close
       if auto_width?
-        @column_widths.each do |num, width|
+        @column_widths.transform_values!{ |width| width || DEF_COL_WIDTH }.each do |num, width|
           set_column_width(num, width + 0.2)
         end
       end
diff --git a/test/auto_width_test.rb b/test/auto_width_test.rb
index a142298..acdc385 100644
--- a/test/auto_width_test.rb
+++ b/test/auto_width_test.rb
@@ -16,4 +16,24 @@
 
     assert_equal(sheet.calculated_column_widths, {0 => 3.52, 1 => 5.28, 2 => 14.96, 3 => 44.88})
   end
+
+  it "should set the default column width for an empty column on close" do
+    workbook = FastExcel.open(constant_memory: false)
+    sheet = workbook.add_worksheet
+    sheet.auto_width = true
+
+    sheet.append_row([
+      nil,
+      "tini",
+      "Longer",
+      "Some longer text!",
+      "This gem is FFI binding for libxlsxwriter C library"
+    ])
+
+    assert_equal(sheet.calculated_column_widths, {0 => nil, 1 => 3.52, 2 => 5.28, 3 => 14.96, 4 => 44.88})
+
+    workbook.close
+
+    assert_equal(sheet.calculated_column_widths, {0 => FastExcel::DEF_COL_WIDTH, 1 => 3.52, 2 => 5.28, 3 => 14.96, 4 => 44.88})
+  end
 end