diff --git a/Library/Homebrew/extend/ENV/super.rb b/Library/Homebrew/extend/ENV/super.rb
index f89b89b367..57d07c637b 100644
--- a/Library/Homebrew/extend/ENV/super.rb
+++ b/Library/Homebrew/extend/ENV/super.rb
@@ -82,6 +82,7 @@ module Superenv
     self['CMAKE_INCLUDE_PATH'] = determine_cmake_include_path
     self['CMAKE_LIBRARY_PATH'] = determine_cmake_library_path
     self['ACLOCAL_PATH'] = determine_aclocal_path
+    self['M4'] = MacOS.locate("m4") if deps.include? "autoconf"
 
     # The HOMEBREW_CCCFG ENV variable is used by the ENV/cc tool to control
     # compiler flag stripping. It consists of a string of characters which act