--- a/src/apprentice.c	2020-11-13 11:14:12 +0100
+++ b/src/apprentice.c	2020-11-13 11:14:21 +0100
@@ -1461,7 +1461,10 @@
 		 */
 		set_last_default(ms, mset[j].me, mset[j].count);
 
-		/* coalesce per file arrays into a single one */
+		/* coalesce per file arrays into a single one, if needed */
+		if (mset[j].count == 0)
+		  continue;
+
 		if (coalesce_entries(ms, mset[j].me, mset[j].count,
 		    &map->magic[j], &map->nmagic[j]) == -1) {
 			errs++;