diff --git a/src/match.c b/src/match.c
index ecab28c..ceb317c 100644
--- a/src/match.c
+++ b/src/match.c
@@ -50,19 +50,28 @@
 	semsg(_(e_invalid_id_nr_must_be_greater_than_or_equal_to_one_1), id);
 	return -1;
     }
-    if (id != -1)
+    if (id == -1)
     {
-	cur = wp->w_match_head;
-	while (cur != NULL)
-	{
+	// use the next available match ID
+	id = wp->w_next_match_id++;
+    }
+    else
+    {
+	// check the given ID is not already in use
+	for (cur = wp->w_match_head; cur != NULL; cur = cur->mit_next)
 	    if (cur->mit_id == id)
 	    {
 		semsg(_(e_id_already_taken_nr), id);
 		return -1;
 	    }
-	    cur = cur->mit_next;
-	}
+
+	// Make sure the next match ID is always higher than the highest
+	// manually selected ID.  Add some extra in case a few more IDs are
+	// added soon.
+	if (wp->w_next_match_id < id + 100)
+	    wp->w_next_match_id = id + 100;
     }
+
     if ((hlg_id = syn_namen2id(grp, (int)STRLEN(grp))) == 0)
     {
 	semsg(_(e_no_such_highlight_group_name_str), grp);
@@ -74,17 +83,6 @@
 	return -1;
     }
 
-    // Find available match ID.
-    while (id == -1)
-    {
-	cur = wp->w_match_head;
-	while (cur != NULL && cur->mit_id != wp->w_next_match_id)
-	    cur = cur->mit_next;
-	if (cur == NULL)
-	    id = wp->w_next_match_id;
-	wp->w_next_match_id++;
-    }
-
     // Build new match.
     m = ALLOC_CLEAR_ONE(matchitem_T);
     if (m == NULL)