diff --git a/Library/Homebrew/mktemp.rb b/Library/Homebrew/mktemp.rb
index e5e0277e2c..ac58541b08 100644
--- a/Library/Homebrew/mktemp.rb
+++ b/Library/Homebrew/mktemp.rb
@@ -40,7 +40,7 @@ class Mktemp
   end
 
   def run
-    @tmpdir = Pathname.new(Dir.mktmpdir("#{@prefix}-", HOMEBREW_TEMP))
+    @tmpdir = Pathname.new(Dir.mktmpdir("#{@prefix.tr "@", "-"}-", HOMEBREW_TEMP))
 
     # Make sure files inside the temporary directory have the same group as the
     # brew instance.