diff --git a/src/tools/fixup_tos_boot_checksum/fixup_tos_floppy_chksum.c b/src/tools/fixup_tos_boot_checksum/fixup_tos_floppy_chksum.c
new file mode 100644
index 0000000000..87fe8c9932
--- /dev/null
+++ b/src/tools/fixup_tos_boot_checksum/fixup_tos_floppy_chksum.c
@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdint.h>
+#include <fcntl.h>
+
+uint8_t sector[512];
+
+int main(int argc, char **argv)
+{
+	int fd, i;
+	uint16_t sum;
+	uint8_t *p = sector;
+	fd = open(argv[1], O_RDWR);
+	if (fd < 0) {
+		return 1;
+	}
+	if (read(fd, sector, 512-2) < 512-2) {
+		perror("read");
+		return 1;
+	}
+	for (sum = 0, i = 0; i < (512-2)/2; i++) {
+		uint16_t v;
+		v = *p++ << 8;
+		v += *p++;
+		sum += v;
+	}
+	sum = 0x1234 - sum /*+ 1*/;
+	//sum = 0xaa55;
+	// big endian
+	*p++ = (uint8_t)(sum >> 8);
+	*p++ = (uint8_t)sum;
+	//lseek(fd, 0LL, SEEK_SET);
+	write(fd, &sector[512-2], 2);
+	return 0;
+}