diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index 3199df2ac5..0b9355d580 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -341,6 +341,8 @@ module Homebrew
       alias generic_check_tmpdir_sticky_bit check_tmpdir_sticky_bit
 
       def check_exist_directories
+        return if HOMEBREW_PREFIX.writable_real?
+
         not_exist_dirs = Keg::MUST_EXIST_DIRECTORIES.reject(&:exist?)
         return if not_exist_dirs.empty?