diff --git a/docs/libcurl/opts/CURLOPT_INFILESIZE.3 b/docs/libcurl/opts/CURLOPT_INFILESIZE.3
index 4a52b503d3..86961de5e8 100644
--- a/docs/libcurl/opts/CURLOPT_INFILESIZE.3
+++ b/docs/libcurl/opts/CURLOPT_INFILESIZE.3
@@ -42,6 +42,9 @@ mandatory.
 
 To unset this value again, set it to -1.
 
+Using \fICURLOPT_UPLOAD(3)\fP to a HTTP/1.1 server and this value set to -1,
+makes libcurl do a chunked transfer-encoded upload.
+
 When sending emails using SMTP, this command can be used to specify the
 optional SIZE parameter for the MAIL FROM command.