diff --git a/fs/ext4/ext4fs.c b/fs/ext4/ext4fs.c
index 85dc122..e2b740c 100644
--- a/fs/ext4/ext4fs.c
+++ b/fs/ext4/ext4fs.c
@@ -66,13 +66,15 @@
 
 	ext_cache_init(&cache);
 
-	if (blocksize <= 0)
-		return -1;
-
 	/* Adjust len so it we can't read past the end of the file. */
 	if (len + pos > filesize)
 		len = (filesize - pos);
 
+	if (blocksize <= 0 || len <= 0) {
+		ext_cache_fini(&cache);
+		return -1;
+	}
+
 	blockcnt = lldiv(((len + pos) + blocksize - 1), blocksize);
 
 	for (i = lldiv(pos, blocksize); i < blockcnt; i++) {