diff --git a/docs/src/mainpage.dox b/docs/src/mainpage.dox
index 6821c4a3..62239868 100644
--- a/docs/src/mainpage.dox
+++ b/docs/src/mainpage.dox
@@ -9,6 +9,9 @@
 
 @section mainpage_intro libxlsxwriter
 
+Note: this is preliminary documentation. The libxlsxwriter library isn't
+released yet.
+
 Libxlsxwriter is a C library that can be used to write text, numbers and
 formulas to multiple worksheets in an Excel 2007+ XLSX file. It supports
 features such as: