diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 2fce4e53442..4251113f2b7 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -645,7 +645,7 @@ as internal buffering of data.
 .. function:: closerange(fd_low, fd_high)
 
    Close all file descriptors from *fd_low* (inclusive) to *fd_high* (exclusive),
-   ignoring errors. Equivalent to::
+   ignoring errors. Equivalent to (but much faster than)::
 
       for fd in range(fd_low, fd_high):
           try:
@@ -729,6 +729,7 @@ as internal buffering of data.
 
    Availability: Unix, Windows.
 
+
 .. function:: fstatvfs(fd)
 
    Return information about the filesystem containing the file associated with file