diff --git a/CHANGELOG b/CHANGELOG
index a1a295fa..4a5654c3 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -8,6 +8,7 @@
   * Accept the tmpdir_root option in Roo::Excelx
   * Change the tmpdir prefix from oo_ to roo_
   * In Excelx, load styles, shared strings and the workbook lazily. Leave the tmpdir open so that reading may take place after initialize. The OS will be responsible for cleaning it up.
+  * Lazily initialize @default_sheet, to avoid reading the sheets earlier than necessary. Use the #default_sheet accessor instead.
 
 * bugfixes
   * Fix that paths with spaces in them would fail with
diff --git a/lib/roo/base.rb b/lib/roo/base.rb
index 5cf3137b..ebb6b8c7 100644
--- a/lib/roo/base.rb
+++ b/lib/roo/base.rb
@@ -21,7 +21,7 @@ class Roo::Base
   TEMP_PREFIX = "roo_"
   LETTERS = ('A'..'Z').to_a
 
-  attr_reader :default_sheet, :headers
+  attr_reader :headers
 
   # sets the line with attribute names (default: 1)
   attr_accessor :header_line
@@ -92,7 +92,10 @@ def initialize(filename, options={}, file_warning=:error, tmpdir=nil)
     @last_column = {}
 
     @header_line = 1
-    @default_sheet = self.sheets.first
+  end
+
+  def default_sheet
+    @default_sheet ||= self.sheets.first
   end
 
   # sets the working sheet in the document
@@ -116,7 +119,7 @@ def last_column_as_letter(sheet=nil)
 
   # returns the number of the first non-empty row
   def first_row(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @first_row[sheet] ||=
       begin
@@ -131,7 +134,7 @@ def first_row(sheet=nil)
 
   # returns the number of the last non-empty row
   def last_row(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @last_row[sheet] ||=
       begin
@@ -146,7 +149,7 @@ def last_row(sheet=nil)
 
   # returns the number of the first non-empty column
   def first_column(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @first_column[sheet] ||=
       begin
@@ -161,7 +164,7 @@ def first_column(sheet=nil)
 
   # returns the number of the last non-empty column
   def last_column(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @last_column[sheet] ||=
       begin
@@ -178,7 +181,7 @@ def last_column(sheet=nil)
   # you can add additional attributes with the prefix parameter like:
   # oo.to_yaml({"file"=>"flightdata_2007-06-26", "sheet" => "1"})
   def to_yaml(prefix={}, from_row=nil, from_column=nil, to_row=nil, to_column=nil,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     return '' unless first_row # empty result if there is no first_row in a sheet
 
     from_row ||= first_row(sheet)
@@ -210,7 +213,7 @@ def to_yaml(prefix={}, from_row=nil, from_column=nil, to_row=nil, to_column=nil,
 
   # write the current spreadsheet to stdout or into a file
   def to_csv(filename=nil,sheet=nil,separator=',')
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     if filename
       File.open(filename,"w") do |file|
         write_csv_content(file,sheet,separator)
@@ -228,7 +231,7 @@ def to_csv(filename=nil,sheet=nil,separator=',')
   def to_matrix(from_row=nil, from_column=nil, to_row=nil, to_column=nil,sheet=nil)
     require 'matrix'
 
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     return Matrix.empty unless first_row
 
     from_row ||= first_row(sheet)
@@ -267,7 +270,7 @@ def find(*args) # :nodoc
   # returns all values in this row as an array
   # row numbers are 1,2,3,... like in the spreadsheet
   def row(rownumber,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     first_column(sheet).upto(last_column(sheet)).map do |col|
       cell(rownumber,col,sheet)
@@ -280,7 +283,7 @@ def column(columnnumber,sheet=nil)
     if columnnumber.class == String
       columnnumber = self.class.letter_to_number(columnnumber)
     end
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     first_row(sheet).upto(last_row(sheet)).map do |row|
       cell(row,columnnumber,sheet)
@@ -290,7 +293,7 @@ def column(columnnumber,sheet=nil)
   # set a cell to a certain value
   # (this will not be saved back to the spreadsheet file!)
   def set(row,col,value,sheet=nil) #:nodoc:
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row, col = normalize(row,col)
     cell_type =
@@ -307,14 +310,14 @@ def set(row,col,value,sheet=nil) #:nodoc:
 
   # reopens and read a spreadsheet document
   def reload
-    ds = @default_sheet
+    ds = default_sheet
     reinitialize
     self.default_sheet = ds
   end
 
   # true if cell is empty
   def empty?(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     contents = cell(row, col, sheet)
@@ -395,8 +398,8 @@ def method_missing(m, *args)
   # access different worksheets by calling spreadsheet.sheet(1)
   # or spreadsheet.sheet('SHEETNAME')
   def sheet(index,name=false)
-    @default_sheet = String === index ? index : self.sheets[index]
-    name ? [@default_sheet,self] : self
+    default_sheet = String === index ? index : self.sheets[index]
+    name ? [default_sheet,self] : self
   end
 
   # iterate through all worksheets of a document
@@ -438,7 +441,7 @@ def each(options={})
       if options[:clean]
         options.delete(:clean)
         @cleaned ||= {}
-        @cleaned[@default_sheet] || clean_sheet(@default_sheet)
+        @cleaned[default_sheet] || clean_sheet(default_sheet)
       end
 
       if options[:header_search]
@@ -640,12 +643,12 @@ def header_index(query)
   end
 
   def set_value(row,col,value,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     @cell[sheet][[row,col]] = value
   end
 
   def set_type(row,col,type,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     @cell_type[sheet][[row,col]] = type
   end
 
diff --git a/lib/roo/csv.rb b/lib/roo/csv.rb
index 082b98a2..cb2e6ef2 100644
--- a/lib/roo/csv.rb
+++ b/lib/roo/csv.rb
@@ -25,13 +25,13 @@ def sheets
   end
 
   def cell(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @cell[normalize(row,col)]
   end
 
   def celltype(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @cell_type[normalize(row,col)]
   end
@@ -69,7 +69,7 @@ def each_row(options, &block)
   end
 
   def read_cells(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     return if @cells_read[sheet]
     @first_row[sheet] = 1
     @last_row[sheet] = 0
diff --git a/lib/roo/excelx.rb b/lib/roo/excelx.rb
index 65ddb171..64637a02 100644
--- a/lib/roo/excelx.rb
+++ b/lib/roo/excelx.rb
@@ -144,7 +144,7 @@ def method_missing(m,*args)
     # is method name a label name
     read_labels
     if @label.has_key?(m.to_s)
-      sheet ||= @default_sheet
+      sheet ||= default_sheet
       read_cells(sheet)
       row,col = label(m.to_s)
       cell(row,col)
@@ -155,7 +155,7 @@ def method_missing(m,*args)
   end
 
   def sheet_for(sheet)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     validate_sheet!(sheet)
     n = self.sheets.index(sheet)
 
@@ -167,7 +167,7 @@ def sheet_for(sheet)
   # (1,1), (1,'A'), ('A',1), ('a',1) all refers to the
   # cell at the first line and first row.
   def cell(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     sheet_object = sheet_for(sheet)
     read_cells(sheet)
     row,col = key = normalize(row,col)
@@ -188,7 +188,7 @@ def cell(row, col, sheet=nil)
   # Returns nil if there is no formula.
   # The method #formula? checks if there is a formula.
   def formula(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     @formula[sheet][[row,col]] && @formula[sheet][[row,col]]
@@ -198,7 +198,7 @@ def formula(row,col,sheet=nil)
     # returns each formula in the selected sheet as an array of elements
   # [row, col, formula]
   def formulas(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     if @formula[sheet]
       @formula[sheet].map do |coord, formula|
@@ -227,7 +227,7 @@ def underline?
 
   # Given a cell, return the cell's style
   def font(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     style_definitions[@style[sheet][[row,col]].to_i]
@@ -242,7 +242,7 @@ def font(row, col, sheet=nil)
   # * :time
   # * :datetime
   def celltype(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     sheet_object = sheet_for(sheet)
 
@@ -261,7 +261,7 @@ def celltype(row,col,sheet=nil)
   # * :string
   # Note: this is only available within the Excelx class
   def excelx_type(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     @excelx_type[sheet][[row,col]]
@@ -270,7 +270,7 @@ def excelx_type(row,col,sheet=nil)
   # returns the internal value of an excelx cell
   # Note: this is only available within the Excelx class
   def excelx_value(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     @excelx_value[sheet][[row,col]]
@@ -278,7 +278,7 @@ def excelx_value(row,col,sheet=nil)
 
   # returns the internal format of an excel cell
   def excelx_format(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     style_format(@style[sheet][[row,col]]).to_s
@@ -294,7 +294,7 @@ def sheets
   # shows the internal representation of all cells
   # for debugging purposes
   def to_s(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @cell[sheet].inspect
   end
@@ -315,7 +315,7 @@ def label(labelname)
   # Returns an array which all labels. Each element is an array with
   # [labelname, [row,col,sheetname]]
   def labels
-    # sheet ||= @default_sheet
+    # sheet ||= default_sheet
     # read_cells(sheet)
     read_labels
     @label.map do |label|
@@ -491,7 +491,7 @@ def read_cell_from_xml(sheet, cell_xml)
 
   # read all cells in the selected sheet
   def read_cells(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     validate_sheet!(sheet)
     return if @cells_read[sheet]
 
diff --git a/lib/roo/open_office.rb b/lib/roo/open_office.rb
index 0666f6c9..731854b8 100644
--- a/lib/roo/open_office.rb
+++ b/lib/roo/open_office.rb
@@ -67,7 +67,7 @@ def method_missing(m,*args)
   # (1,1), (1,'A'), ('A',1), ('a',1) all refers to the
   # cell at the first line and first row.
   def cell(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     if celltype(row,col,sheet) == :date
@@ -81,7 +81,7 @@ def cell(row, col, sheet=nil)
   # Returns nil if there is no formula.
   # The method #formula? checks if there is a formula.
   def formula(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     @formula[sheet][[row,col]]
@@ -91,7 +91,7 @@ def formula(row,col,sheet=nil)
   # returns each formula in the selected sheet as an array of elements
   # [row, col, formula]
   def formulas(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     if @formula[sheet]
       @formula[sheet].each.collect do |elem|
@@ -120,7 +120,7 @@ def underline?
 
   # Given a cell, return the cell's style
   def font(row, col, sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     style_name = @style[sheet][[row,col]] || @style_defaults[sheet][col - 1] || 'Default'
@@ -136,7 +136,7 @@ def font(row, col, sheet=nil)
   # * :time
   # * :datetime
   def celltype(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     if @formula[sheet][[row,col]]
@@ -162,7 +162,7 @@ def officeversion
   # shows the internal representation of all cells
   # mainly for debugging purposes
   def to_s(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     @cell[sheet].inspect
   end
@@ -199,7 +199,7 @@ def labels(sheet=nil)
   # returns the comment at (row/col)
   # nil if there is no comment
   def comment(row,col,sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_cells(sheet)
     row,col = normalize(row,col)
     return nil unless @comment[sheet]
@@ -209,7 +209,7 @@ def comment(row,col,sheet=nil)
   # returns each comment in the selected sheet as an array of elements
   # [row, col, comment]
   def comments(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     read_comments(sheet) unless @comments_read[sheet]
     if @comment[sheet]
       @comment[sheet].each.collect do |elem|
@@ -277,7 +277,7 @@ def set_cell_values(sheet,x,y,i,v,value_type,formula,table_cell,str_v,style_name
   # some content <text:s text:c="3"/>
   #++
   def read_cells(sheet=nil)
-    sheet ||= @default_sheet
+    sheet ||= default_sheet
     validate_sheet!(sheet)
     return if @cells_read[sheet]
 
diff --git a/test/test_generic_spreadsheet.rb b/test/test_generic_spreadsheet.rb
index cbb26160..53301f8d 100644
--- a/test/test_generic_spreadsheet.rb
+++ b/test/test_generic_spreadsheet.rb
@@ -15,12 +15,12 @@ def read_cells(sheet=nil)
       end
 
       def cell(row, col, sheet=nil)
-        sheet ||= @default_sheet
+        sheet ||= default_sheet
         @cell[sheet][[row,col]]
       end
 
       def celltype(row, col, sheet=nil)
-        sheet ||= @default_sheet
+        sheet ||= default_sheet
         @cell_type[sheet][[row,col]]
       end
 
diff --git a/test/test_roo.rb b/test/test_roo.rb
index 7d34bcdf..d2bac112 100644
--- a/test/test_roo.rb
+++ b/test/test_roo.rb
@@ -1003,18 +1003,18 @@ def test_file_warning_error
 
   def test_file_warning_warning
     if OPENOFFICE
-        assert_raises(Errno::ENOENT) {
-          Roo::OpenOffice.new(File.join(TESTDIR,"numbers1.xlsx"),
-          packed: false,
-          file_warning: :warning)
-        }
+      assert_raises(Errno::ENOENT) {
+        Roo::OpenOffice.new(File.join(TESTDIR,"numbers1.xlsx"),
+        packed: false,
+        file_warning: :warning)
+      }
     end
     if EXCELX
-        assert_raises(Errno::ENOENT) {
-          Roo::Excelx.new(File.join(TESTDIR,"numbers1.ods"),
-          packed: false,
-          file_warning: :warning)
-        }
+      assert_nothing_raised {
+        Roo::Excelx.new(File.join(TESTDIR,"numbers1.ods"),
+        packed: false,
+        file_warning: :warning)
+      }
     end
   end