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)) {
@@ -611,7 +618,8 @@
 		return (EINVAL);
 	}
 
-	if (le32toh(es->e2fs_first_dblock) >= fs->e2fs_bcount) {
+	if (le32toh(es->e2fs_first_dblock) != (fs->e2fs_bsize > 1024 ? 0 : 1) ||
+	    le32toh(es->e2fs_first_dblock) >= fs->e2fs_bcount) {
 		SDT_PROBE1(ext2fs, , vfsops, ext2_compute_sb_data_error,
 		    "first data block out of range");
 		return (EINVAL);