diff --git a/Library/Homebrew/extend/pathname.rb b/Library/Homebrew/extend/pathname.rb
index df32e8870d..1f384db734 100644
--- a/Library/Homebrew/extend/pathname.rb
+++ b/Library/Homebrew/extend/pathname.rb
@@ -181,20 +181,20 @@ class Pathname
     # POSIX tar magic has a 257 byte offset
     # magic numbers stolen from /usr/share/file/magic/
     case open { |f| f.read(262) }
-    when /^PK\003\004/n   then :zip
-    when /^\037\213/n     then :gzip
-    when /^BZh/n          then :bzip2
-    when /^\037\235/n     then :compress
-    when /^.{257}ustar/n  then :tar
-    when /^\xFD7zXZ\x00/n then :xz
-    when /^Rar!/n         then :rar
+    when /^PK\003\004/n         then :zip
+    when /^\037\213/n           then :gzip
+    when /^BZh/n                then :bzip2
+    when /^\037\235/n           then :compress
+    when /^.{257}ustar/n        then :tar
+    when /^\xFD7zXZ\x00/n       then :xz
+    when /^Rar!/n               then :rar
+    when /^7z\xBC\xAF\x27\x1C/n then :p7zip
     else
       # This code so that bad-tarballs and zips produce good error messages
       # when they don't unarchive properly.
       case extname
-        when ".tar.gz", ".tgz", ".tar.bz2", ".tbz" then :tar
-        when ".zip" then :zip
-        when ".7z" then :p7zip
+      when ".tar.gz", ".tgz", ".tar.bz2", ".tbz" then :tar
+      when ".zip" then :zip
       end
     end
   end