diff --git a/doc/PreprocessorDirectives.dox b/doc/PreprocessorDirectives.dox
index d801798c9..7e9e30c4b 100644
--- a/doc/PreprocessorDirectives.dox
+++ b/doc/PreprocessorDirectives.dox
@@ -78,6 +78,7 @@ functions by defining EIGEN_HAS_C99_MATH=1.
    Automatic detection disabled if EIGEN_MAX_CPP_VER<11.
  - \b EIGEN_HAS_CXX11_NOEXCEPT - defines whether noexcept is supported
    Automatic detection disabled if EIGEN_MAX_CPP_VER<11.
+ - \b EIGEN_NO_IO - Disables any usage and support for `<iostreams>`.
 
 \section TopicPreprocessorDirectivesAssertions Assertions