diff --git a/doc/airline.txt b/doc/airline.txt
index 77a27e99..6b59051c 100644
--- a/doc/airline.txt
+++ b/doc/airline.txt
@@ -124,9 +124,13 @@ CUSTOMIZATION                                        *airline-customization*
 The following are some unicode symbols for customizing the left/right
 separators, as well as the powerline font glyths.
 
-Note: You must define the dictionary first before setting values: >
-  let g:airline_symbols = {}
->
+Note: You must define the dictionary first before setting values. Also, it's a
+good idea to check whether if it exists as to avoid accidentally overwritting
+its contents. >
+  if !exists('g:airline_symbols')
+    let g:airline_symbols = {}
+  endif
+
   " unicode symbols
   let g:airline_left_sep = '»'
   let g:airline_left_sep = '▶'