diff --git a/Doc/library/readline.rst b/Doc/library/readline.rst
index 5658b93c81d..d03b7159713 100644
--- a/Doc/library/readline.rst
+++ b/Doc/library/readline.rst
@@ -45,6 +45,10 @@ Readline library in general.
     python:bind -v
     python:bind ^I rl_complete
 
+  Also note that different libraries may use different history file formats.
+  When switching the underlying library, existing history files may become
+  unusable.
+
 .. data:: backend
 
    The name of the underlying Readline library being used, either