diff --git a/lib/Target/Mips/MipsSubtarget.h b/lib/Target/Mips/MipsSubtarget.h
index 3193369..77bd31c 100644
--- a/lib/Target/Mips/MipsSubtarget.h
+++ b/lib/Target/Mips/MipsSubtarget.h
@@ -27,6 +27,7 @@
 class MipsSubtarget : public MipsGenSubtargetInfo {
 
 public:
+  // NOTE: O64 will not be supported.
   enum MipsABIEnum {
     O32, N32, N64, EABI
   };