diff --git a/Doc/includes/typestruct.h b/Doc/includes/typestruct.h
index 50c4621..9f47899 100644
--- a/Doc/includes/typestruct.h
+++ b/Doc/includes/typestruct.h
@@ -9,7 +9,8 @@
     printfunc tp_print;
     getattrfunc tp_getattr;
     setattrfunc tp_setattr;
-    PyAsyncMethods *tp_as_async; /* formerly known as tp_compare or tp_reserved */
+    PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
+                                    or tp_reserved (Python 3) */
     reprfunc tp_repr;
 
     /* Method suites for standard classes */
diff --git a/Include/object.h b/Include/object.h
index 8afcbe9..4d286ef 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -351,7 +351,8 @@
     printfunc tp_print;
     getattrfunc tp_getattr;
     setattrfunc tp_setattr;
-    PyAsyncMethods *tp_as_async; /* formerly known as tp_compare or tp_reserved */
+    PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
+                                    or tp_reserved (Python 3) */
     reprfunc tp_repr;
 
     /* Method suites for standard classes */