diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml
index e3c1539a1e3..d0dbf017a9e 100644
--- a/doc/src/sgml/indexam.sgml
+++ b/doc/src/sgml/indexam.sgml
@@ -141,7 +141,7 @@ typedef struct IndexAmRoutine
     ambuild_function ambuild;
     ambuildempty_function ambuildempty;
     aminsert_function aminsert;
-    aminsertcleanup_function aminsertcleanup;
+    aminsertcleanup_function aminsertcleanup;   /* can be NULL */
     ambulkdelete_function ambulkdelete;
     amvacuumcleanup_function amvacuumcleanup;
     amcanreturn_function amcanreturn;   /* can be NULL */
diff --git a/src/include/access/amapi.h b/src/include/access/amapi.h
index d3e5e5d5918..09801450816 100644
--- a/src/include/access/amapi.h
+++ b/src/include/access/amapi.h
@@ -271,7 +271,7 @@ typedef struct IndexAmRoutine
 	ambuild_function ambuild;
 	ambuildempty_function ambuildempty;
 	aminsert_function aminsert;
-	aminsertcleanup_function aminsertcleanup;
+	aminsertcleanup_function aminsertcleanup;	/* can be NULL */
 	ambulkdelete_function ambulkdelete;
 	amvacuumcleanup_function amvacuumcleanup;
 	amcanreturn_function amcanreturn;	/* can be NULL */