diff --git a/Library/Homebrew/extend/ENV.rb b/Library/Homebrew/extend/ENV.rb
index 3b2da74c7f..1edc4a64bb 100644
--- a/Library/Homebrew/extend/ENV.rb
+++ b/Library/Homebrew/extend/ENV.rb
@@ -183,11 +183,11 @@ module HomebrewEnvExtension
 
   def m64
     append_to_cflags '-m64'
-    ENV['LDFLAGS'] += '-arch x86_64'
+    ENV.append 'LDFLAGS', '-arch x86_64'
   end
   def m32
     append_to_cflags '-m32'
-    ENV['LDFLAGS'] += '-arch i386'
+    ENV.append 'LDFLAGS', '-arch i386'
   end
 
   # i386 and x86_64 only, no PPC