diff --git a/sys/ufs/ffs/ffs_subr.c b/sys/ufs/ffs/ffs_subr.c
--- a/sys/ufs/ffs/ffs_subr.c
+++ b/sys/ufs/ffs/ffs_subr.c
@@ -43,6 +43,7 @@
 #include <stdlib.h>
 #include <time.h>
 #include <sys/errno.h>
+#include <sys/endian.h>
 #include <ufs/ufs/dinode.h>
 #include <ufs/ffs/fs.h>
 
@@ -382,6 +383,18 @@
 	prtmsg = ((flags & UFS_NOMSG) == 0);
 	warnerr = (flags & UFS_NOWARNFAIL) == UFS_NOWARNFAIL ? 0 : ENOENT;
 	wmsg = warnerr ? "" : " (Ignored)";
+
+	/* Guess endian mismatch between machine and filesystem */
+	if ((fs->fs_magic != FS_UFS2_MAGIC) &&
+		(bswap32(fs->fs_magic) == FS_UFS2_MAGIC)) {
+		MPRINT("UFS2 superblock failed: possible endian mismatch between machine and filesystem\n");
+		return(ENOEXEC);
+	} else if ((fs->fs_magic != FS_UFS1_MAGIC) &&
+			 (bswap32(fs->fs_magic) == FS_UFS1_MAGIC)) {
+		MPRINT("UFS1 superblock failed: possible endian mismatch between machine and filesystem\n");
+		return(ENOEXEC);
+	}
+
 	/*
 	 * If just validating for recovery, then do just the minimal
 	 * checks needed for the superblock fields needed to find