diff --git a/ftplugin/sass.vim b/ftplugin/sass.vim
index 6d0fbc9..c7a39e5 100644
--- a/ftplugin/sass.vim
+++ b/ftplugin/sass.vim
@@ -8,9 +8,10 @@ if exists("b:did_ftplugin")
 endif
 let b:did_ftplugin = 1
 
-let b:undo_ftplugin = "setl cms< inc< inex< ofu< sua<"
+let b:undo_ftplugin = "setl cms< def< inc< inex< ofu< sua<"
 
 setlocal commentstring=//\ %s
+setlocal define=^\\s*\\%(@mixin\\\|=\\)
 setlocal includeexpr=substitute(v:fname,'\\%(.*/\\\|^\\)\\zs','_','')
 setlocal omnifunc=csscomplete#CompleteCSS
 setlocal suffixesadd=.sass,.scss,.css