Index: sys/fs/ext2fs/ext2_vfsops.c
===================================================================
--- sys/fs/ext2fs/ext2_vfsops.c
+++ sys/fs/ext2fs/ext2_vfsops.c
@@ -465,6 +465,13 @@
 	int g_count = 0;
 	int error;
 
+	/* Check if first dblock is valid */
+	if (fs->e2fs->e2fs_bcount >= 1024 && fs->e2fs->e2fs_first_dblock) {
+		SDT_PROBE1(ext2fs, , vfsops, ext2_compute_sb_data_error,
+		    "first dblock is invalid");
+		return (EINVAL);
+	}
+
 	/* Check checksum features */
 	if (EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_GDT_CSUM) &&
 	    EXT2_HAS_RO_COMPAT_FEATURE(fs, EXT2F_ROCOMPAT_METADATA_CKSUM)) {