diff --git a/Library/Homebrew/cmd/tap.rb b/Library/Homebrew/cmd/tap.rb
index 13d9290e368d..6d1a596a6087 100644
--- a/Library/Homebrew/cmd/tap.rb
+++ b/Library/Homebrew/cmd/tap.rb
@@ -1,4 +1,3 @@
-require 'tempfile'
 
 HOMEBREW_LIBRARY = HOMEBREW_REPOSITORY/"Library"
 
@@ -43,10 +42,7 @@ def link_tap_formula formulae
       end
     end
 
-    tf = Tempfile.new("brew-tap")
-    tf.write(ignores.uniq.join("\n"))
-    tf.close
-    mv tf.path, "#{HOMEBREW_LIBRARY}/Formula/.gitignore"
+    HOMEBREW_LIBRARY.join("Formula/.gitignore").atomic_write(ignores.uniq.join("\n"))
   end
 
   private
diff --git a/Library/Homebrew/cmd/untap.rb b/Library/Homebrew/cmd/untap.rb
index 80d38934b000..92faf3069db8 100644
--- a/Library/Homebrew/cmd/untap.rb
+++ b/Library/Homebrew/cmd/untap.rb
@@ -1,5 +1,4 @@
-require 'cmd/tap' # for Pathname.recursive_formula
-require 'tempfile'
+require 'cmd/tap' # for tap_args
 
 module Homebrew extend self
   def untap
@@ -18,9 +17,6 @@ def untap
     end
     rm_rf tapd
 
-    tf = Tempfile.new("brew-untap")
-    tf.write(gitignores.join("\n"))
-    tf.close
-    mv tf.path, "#{HOMEBREW_PREFIX}/Library/Formula/.gitignore"
+    HOMEBREW_REPOSITORY.join("Library/Formula/.gitignore").atomic_write(gitignores * "\n")
   end
 end
diff --git a/Library/Homebrew/extend/pathname.rb b/Library/Homebrew/extend/pathname.rb
index bc58c885fd4a..da195e5a86bc 100644
--- a/Library/Homebrew/extend/pathname.rb
+++ b/Library/Homebrew/extend/pathname.rb
@@ -90,6 +90,15 @@ def write content
     File.open(self, 'w') {|f| f.write content }
   end
 
+  # NOTE always overwrites
+  def atomic_write content
+    require 'tempfile'
+    tf = Tempfile.new(self.basename.to_s)
+    tf.write(content)
+    tf.close
+    FileUtils.mv tf.path, self.to_s
+  end
+
   def cp dst
     if file?
       FileUtils.cp to_s, dst