diff --git a/src/hb-open-type.hh b/src/hb-open-type.hh
index 3c6625376..dc0ae1d98 100644
--- a/src/hb-open-type.hh
+++ b/src/hb-open-type.hh
@@ -62,6 +62,8 @@ struct IntType
   IntType () = default;
   explicit constexpr IntType (Type V) : v {V} {}
   IntType& operator = (Type i) { v = i; return *this; }
+  /* For reason we define cast out operator for signed/unsigned, instead of Type, see:
+   * https://github.com/harfbuzz/harfbuzz/pull/2875/commits/09836013995cab2b9f07577a179ad7b024130467 */
   operator hb_conditional<hb_is_signed (Type), signed, unsigned> () const { return v; }
 
   bool operator == (const IntType &o) const { return (Type) v == (Type) o.v; }