diff --git a/reference/filesystem/functions/popen.xml b/reference/filesystem/functions/popen.xml
index c2b7277ed0..eb51722bd8 100644
--- a/reference/filesystem/functions/popen.xml
+++ b/reference/filesystem/functions/popen.xml
@@ -35,7 +35,14 @@
mode
- The mode
+ The mode. Either 'r' for reading, or 'w'
+ for writing.
+
+
+ On Windows, popen defaults to text mode, i.e. any \n
+ characters written to or read from the pipe will be translated to \r\n.
+ If this is not desired, binaray mode can be enforced by setting mode
+ to 'rb' and 'wb', respectively.