diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index 6c1eea2f1..165397641 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -93,6 +93,9 @@ of bytes actually taken care of. If that amount differs from the amount passed
 to your function, it'll signal an error to the library and it will abort the
 transfer and return \fICURLE_WRITE_ERROR\fP.
 
+This function may be called with zero bytes data if the transfered file is
+empty.
+
 Set the \fIstream\fP argument with the \fICURLOPT_WRITEDATA\fP option.
 
 \fBNOTE:\fP you will be passed as much data as possible in all invokes, but