diff --git a/tools/test/stress2/tools/zapsb.c b/tools/test/stress2/tools/zapsb.c
new file mode 100644
index 000000000000..09e16e27c322
--- /dev/null
+++ b/tools/test/stress2/tools/zapsb.c
@@ -0,0 +1,75 @@
+/*
+ * Zero out a superblock check hash.
+ * By Kirk McKusick <mckusick@mckusick.com>
+ */
+
+#include <sys/param.h>
+#include <sys/disklabel.h>
+
+#include <ufs/ufs/dinode.h>
+#include <ufs/ffs/fs.h>
+
+#include <err.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+
+/*
+ * Possible superblock locations ordered from most to least likely.
+ */
+static int sblock_try[] = SBLOCKSEARCH;
+
+static void
+usage(void)
+{
+	(void)fprintf(stderr, "usage: zapsb special_device\n");
+	exit(1);
+}
+
+int
+main(int argc, char *argv[])
+{
+	char *fs, sblock[SBLOCKSIZE];
+	struct fs *sbp;
+	int i, fd;
+
+	if (argc != 2)
+		usage();
+
+	fs = *++argv;
+
+	/* get the superblock. */
+	if ((fd = open(fs, O_RDWR, 0)) < 0)
+		err(1, "%s", fs);
+	for (i = 0; sblock_try[i] != -1; i++) {
+		if (lseek(fd, (off_t)(sblock_try[i]), SEEK_SET) < 0)
+			err(1, "%s", fs);
+		if (read(fd, sblock, sizeof(sblock)) != sizeof(sblock))
+			errx(1, "%s: can't read superblock", fs);
+		sbp = (struct fs *)sblock;
+		if ((sbp->fs_magic == FS_UFS1_MAGIC ||
+		     (sbp->fs_magic == FS_UFS2_MAGIC &&
+		      sbp->fs_sblockloc == sblock_try[i])) &&
+		    sbp->fs_bsize <= MAXBSIZE &&
+		    sbp->fs_bsize >= (int)sizeof(struct fs))
+			break;
+	}
+	if (sblock_try[i] == -1) {
+		fprintf(stderr, "Cannot find file system superblock\n");
+		exit(2);
+	}
+	if ((sbp->fs_metackhash & CK_SUPERBLOCK) == 0) {
+		fprintf(stderr, "file system superblock has no check hash\n");
+		exit(3);
+	}
+	printf("zeroing superblock checksum at location %d\n", sblock_try[i]);
+	sbp->fs_ckhash = 0;
+	if (lseek(fd, (off_t)(sblock_try[i]), SEEK_SET) < 0)
+		err(1, "%s", fs);
+	if (write(fd, sblock, sizeof(sblock)) != sizeof(sblock))
+		errx(1, "%s: can't write superblock", fs);
+	(void)close(fd);
+	exit(0);
+}