diff --git a/.document b/.document
new file mode 100644
index 0000000..74ac487
--- /dev/null
+++ b/.document
@@ -0,0 +1,4 @@
+BSDL
+COPYING
+README.md
+ext/zlib/zlib.c
diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index d019891..7e319ca 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -1456,6 +1456,7 @@ rb_zstream_finish(VALUE obj)
  * call-seq:
  *   flush_next_in -> input
  *
+ * Flushes input buffer and returns all data in that buffer.
  */
 static VALUE
 rb_zstream_flush_next_in(VALUE obj)