diff --git a/Library/Homebrew/os/mac/hardware.rb b/Library/Homebrew/os/mac/hardware.rb
index 84308b67e6..6b11f6ad50 100644
--- a/Library/Homebrew/os/mac/hardware.rb
+++ b/Library/Homebrew/os/mac/hardware.rb
@@ -8,7 +8,8 @@ module MacCPUs
     :g3 => "-mcpu=750",
     :g4 => "-mcpu=7400",
     :g4e => "-mcpu=7450",
-    :g5 => "-mcpu=970"
+    :g5 => "-mcpu=970",
+    :g5_64 => "-mcpu=970 -arch ppc64"
   }.freeze
   def optimization_flags
     OPTIMIZATION_FLAGS