diff --git a/Library/ENV/4.3/cc b/Library/ENV/4.3/cc
index eeb87e3323..d2c7be0cee 100755
--- a/Library/ENV/4.3/cc
+++ b/Library/ENV/4.3/cc
@@ -262,8 +262,8 @@ class Cmd
     !ENV['VERBOSE'].nil? || !ENV['HOMEBREW_VERBOSE'].nil?
   end
   def configure?
-    # configure scripts generated with autoconf 2.56 or later export DUALCASE
-    ENV.key? 'DUALCASE'
+    # configure scripts generated with autoconf 2.61 or later export as_nl
+    ENV.key? 'as_nl'
   end
 end
 
diff --git a/Library/Homebrew/extend/ENV/super.rb b/Library/Homebrew/extend/ENV/super.rb
index a71e4075c3..889ac58a0f 100644
--- a/Library/Homebrew/extend/ENV/super.rb
+++ b/Library/Homebrew/extend/ENV/super.rb
@@ -53,9 +53,9 @@ module Superenv
     delete('GREP_OPTIONS') # can break CMake
     delete('CLICOLOR_FORCE') # autotools doesn't like this
 
-    # Configure scripts generated by autoconf 2.56 or later export DUALCASE,
-    # which we use as a heuristic for running under configure
-    delete('DUALCASE')
+    # Configure scripts generated by autoconf 2.61 or later export as_nl, which
+    # we use as a heuristic for running under configure
+    delete('as_nl')
   end
 
   def setup_build_environment(formula=nil)