diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 826e504..41b7866 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1444,9 +1444,11 @@ index_drop(Oid indexId, bool concurrent)
 
 		/*
 		 * Now we must wait until no running transaction could be using the
-		 * index for a query. Note we do not need to worry about xacts that
-		 * open the table for reading after this point; they will see the
-		 * index as invalid when they open the relation.
+		 * index for a query. This is done with AccessExclusiveLock to check
+		 * which running transaction has a lock of any kind on the table.
+		 * Note we do not need to worry about xacts that open the table for
+		 * reading after this point; they will see the index as invalid when
+		 * they open the relation.
 		 *
 		 * Note: the reason we use actual lock acquisition here, rather than
 		 * just checking the ProcArray and sleeping, is that deadlock is
diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 2155252..c952bc3 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -651,9 +651,10 @@ DefineIndex(IndexStmt *stmt,
 	 * for an overview of how this works)
 	 *
 	 * Now we must wait until no running transaction could have the table open
-	 * with the old list of indexes. Note we do not need to worry about xacts
-	 * that open the table for writing after this point; they will see the new
-	 * index when they open it.
+	 * with the old list of indexes. This is done with ShareLock to check
+	 * which running transaction holds a lock that permits writing the table.
+	 * Note we do not need to worry about xacts that open the table for
+	 * writing after this point; they will see the new index when they open it.
 	 *
 	 * Note: the reason we use actual lock acquisition here, rather than just
 	 * checking the ProcArray and sleeping, is that deadlock is possible if