diff --git a/serial/serialutil.py b/serial/serialutil.py
index 150f5f2..ce0613c 100644
--- a/serial/serialutil.py
+++ b/serial/serialutil.py
@@ -571,6 +571,9 @@
     # additional functionality
 
     def read_all(self):
+        """\
+        Read all bytes currently available in the buffer of the OS.
+        """
         return self.read(self.in_waiting)
 
     def read_until(self, terminator=LF, size=None):