diff --git a/lib/roo/base.rb b/lib/roo/base.rb
index e6f3bddb..1d91d9cb 100644
--- a/lib/roo/base.rb
+++ b/lib/roo/base.rb
@@ -314,7 +314,7 @@ 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 : sheets[index]
+    self.default_sheet = String === index ? index : sheets[index]
     name ? [default_sheet, self] : self
   end