diff --git a/docs/source/devguide/styleguide.rst b/docs/source/devguide/styleguide.rst
index 25c58ae773..c8644e45cc 100644
--- a/docs/source/devguide/styleguide.rst
+++ b/docs/source/devguide/styleguide.rst
@@ -153,6 +153,8 @@ Avoid extraneous whitespace in the following situations:
     Yes: if (variable == 2) then
     No:  if ( variable==2 ) then
 
+Do not leave trailing whitespace at the end of a line.
+
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 Python
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