diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index c165b1ecf..b169ada0b 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -764,7 +764,7 @@ hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
 						  hb_tag_t      table_tag,
 						  unsigned int  script_index,
 						  unsigned int  language_index,
-						  unsigned int *feature_index)
+						  unsigned int *feature_index /* OUT */)
 {
   return hb_ot_layout_language_get_required_feature (face,
 						     table_tag,
@@ -781,7 +781,7 @@ hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
  * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
  * @script_index: The index of the requested script tag
  * @language_index: The index of the requested language tag
- * @feature_index: The index of the requested feature
+ * @feature_index: (out): The index of the requested feature
  * @feature_tag: (out): The #hb_tag_t of the requested feature
  *
  * Fetches the tag of a requested feature index in the given face's GSUB or GPOS table,
@@ -796,8 +796,8 @@ hb_ot_layout_language_get_required_feature (hb_face_t    *face,
 					    hb_tag_t      table_tag,
 					    unsigned int  script_index,
 					    unsigned int  language_index,
-					    unsigned int *feature_index,
-					    hb_tag_t     *feature_tag)
+					    unsigned int *feature_index /* OUT */,
+					    hb_tag_t     *feature_tag   /* OUT */)
 {
   const OT::GSUBGPOS &g = get_gsubgpos_table (face, table_tag);
   const OT::LangSys &l = g.get_script (script_index).get_lang_sys (language_index);
diff --git a/src/hb-ot-layout.h b/src/hb-ot-layout.h
index c0cb2a523..3625f91d9 100644
--- a/src/hb-ot-layout.h
+++ b/src/hb-ot-layout.h
@@ -161,7 +161,7 @@ HB_EXTERN hb_bool_t
 hb_ot_layout_table_find_script (hb_face_t    *face,
 				hb_tag_t      table_tag,
 				hb_tag_t      script_tag,
-				unsigned int *script_index);
+				unsigned int *script_index /* OUT */);
 
 HB_EXTERN hb_bool_t
 hb_ot_layout_table_select_script (hb_face_t      *face,
@@ -199,15 +199,15 @@ hb_ot_layout_language_get_required_feature_index (hb_face_t    *face,
 						  hb_tag_t      table_tag,
 						  unsigned int  script_index,
 						  unsigned int  language_index,
-						  unsigned int *feature_index);
+						  unsigned int *feature_index /* OUT */);
 
 HB_EXTERN hb_bool_t
 hb_ot_layout_language_get_required_feature (hb_face_t    *face,
 					    hb_tag_t      table_tag,
 					    unsigned int  script_index,
 					    unsigned int  language_index,
-					    unsigned int *feature_index,
-					    hb_tag_t     *feature_tag);
+					    unsigned int *feature_index /* OUT */,
+					    hb_tag_t     *feature_tag /* OUT */);
 
 HB_EXTERN unsigned int
 hb_ot_layout_language_get_feature_indexes (hb_face_t    *face,
@@ -233,7 +233,7 @@ hb_ot_layout_language_find_feature (hb_face_t    *face,
 				    unsigned int  script_index,
 				    unsigned int  language_index,
 				    hb_tag_t      feature_tag,
-				    unsigned int *feature_index);
+				    unsigned int *feature_index /* OUT */);
 
 HB_EXTERN unsigned int
 hb_ot_layout_feature_get_lookups (hb_face_t    *face,