diff --git a/sbin/fsck_msdosfs/dir.c b/sbin/fsck_msdosfs/dir.c
index a57a39ef2018..38c70144d679 100644
--- a/sbin/fsck_msdosfs/dir.c
+++ b/sbin/fsck_msdosfs/dir.c
@@ -621,7 +621,7 @@ readDosDirSection(int f, struct bootblock *boot, struct fatEntry *fat,
 			dirent.name[8] = '\0';
 			for (k = 7; k >= 0 && dirent.name[k] == ' '; k--)
 				dirent.name[k] = '\0';
-			if (dirent.name[k] != '\0')
+			if (k < 0 || dirent.name[k] != '\0')
 				k++;
 			if (dirent.name[0] == SLOT_E5)
 				dirent.name[0] = 0xe5;