diff --git a/src/include/microhttpd.h b/src/include/microhttpd.h
index 5ced10f0..1f8f6d9f 100644
--- a/src/include/microhttpd.h
+++ b/src/include/microhttpd.h
@@ -1394,6 +1394,9 @@ MHD_add_connection (struct MHD_Daemon *daemon,
 
 /**
  * Obtain the `select()` sets for this daemon.
+ * Daemon's FDs will be added to fd_sets. To get only
+ * daemon FDs in fd_sets, call FD_ZERO for each fd_set
+ * before calling this function.
  *
  * @param daemon daemon to get sets from
  * @param read_fd_set read set
diff --git a/src/microhttpd/daemon.c b/src/microhttpd/daemon.c
index 890e4dd8..8227c90b 100644
--- a/src/microhttpd/daemon.c
+++ b/src/microhttpd/daemon.c
@@ -567,6 +567,9 @@ add_to_fd_set (int fd,
 
 /**
  * Obtain the `select()` sets for this daemon.
+ * Daemon's FDs will be added to fd_sets. To get only
+ * daemon FDs in fd_sets, call FD_ZERO for each fd_set
+ * before calling this function.
  *
  * @param daemon daemon to get sets from
  * @param read_fd_set read set