diff --git a/flist.c b/flist.c
index 464d556..087f9da 100644
--- a/flist.c
+++ b/flist.c
@@ -2584,6 +2584,19 @@ struct file_list *recv_file_list(int f, int dir_ndx)
 		init_hard_links();
 #endif
 
+	if (inc_recurse && dir_ndx >= 0) {
+		if (dir_ndx >= dir_flist->used) {
+			rprintf(FERROR_XFER, "rsync: refusing invalid dir_ndx %u >= %u\n", dir_ndx, dir_flist->used);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+		struct file_struct *file = dir_flist->files[dir_ndx];
+		if (file->flags & FLAG_GOT_DIR_FLIST) {
+			rprintf(FERROR_XFER, "rsync: refusing malicious duplicate flist for dir %d\n", dir_ndx);
+			exit_cleanup(RERR_PROTOCOL);
+		}
+		file->flags |= FLAG_GOT_DIR_FLIST;
+	}
+
 	flist = flist_new(0, "recv_file_list");
 	flist_expand(flist, FLIST_START_LARGE);
 
diff --git a/rsync.h b/rsync.h
index f8bd024..fbaf312 100644
--- a/rsync.h
+++ b/rsync.h
@@ -92,6 +92,7 @@
 #define FLAG_SKIP_GROUP (1<<10)	/* receiver/generator */
 #define FLAG_TIME_FAILED (1<<11)/* generator */
 #define FLAG_MOD_NSEC (1<<12)	/* sender/receiver/generator */
+#define FLAG_GOT_DIR_FLIST (1<<13)/* sender/receiver/generator - dir_flist only */
 
 /* These flags are passed to functions but not stored. */