diff --git a/sbin/nvmecontrol/Makefile b/sbin/nvmecontrol/Makefile
index facb5f09835d..e3d363b123ed 100644
--- a/sbin/nvmecontrol/Makefile
+++ b/sbin/nvmecontrol/Makefile
@@ -1,22 +1,21 @@
-
 .include <src.opts.mk>
 
 PACKAGE=nvme-tools
 PROG=	nvmecontrol
 SRCS=	comnd.c nvmecontrol.c
 SRCS+=	devlist.c firmware.c format.c identify.c logpage.c ns.c nsid.c
 SRCS+=	perftest.c power.c reset.c resv.c sanitize.c
 SRCS+=	passthru.c
 SRCS+=	identify_ext.c nvme_util.c nc_util.c
 SRCS+=  selftest.c
 MAN=	nvmecontrol.8
 LDFLAGS+= -rdynamic
 LIBADD+= util
 SUBDIR=	modules
 HAS_TESTS=
 SUBDIR.${MK_TESTS}+= tests
 
 .PATH:	${SRCTOP}/sys/dev/nvme
 
 .include <bsd.prog.mk>
 .include <bsd.subdir.mk>
diff --git a/sbin/nvmecontrol/nvmecontrol.h b/sbin/nvmecontrol/nvmecontrol.h
index ed331327ae9e..4187c9bee432 100644
--- a/sbin/nvmecontrol/nvmecontrol.h
+++ b/sbin/nvmecontrol/nvmecontrol.h
@@ -1,114 +1,125 @@
 /*-
  * SPDX-License-Identifier: BSD-2-Clause
  *
  * Copyright (C) 2012-2013 Intel Corporation
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #ifndef __NVMECONTROL_H__
 #define __NVMECONTROL_H__
 
 #include <dev/nvme/nvme.h>
 #include "comnd.h"
 
 typedef void (*print_fn_t)(const struct nvme_controller_data *cdata, void *buf, uint32_t size);
 
 struct logpage_function {
         SLIST_ENTRY(logpage_function)   link;
 	uint8_t		log_page;
 	const char     *vendor;
 	const char     *name;
 	print_fn_t	print_fn;
 	size_t		size;
 };
 
 #define NVME_LOGPAGE(unique, lp, vend, nam, fn, sz)			\
 	static struct logpage_function unique ## _lpf = {		\
 		.log_page = lp,						\
 		.vendor = vend,						\
 		.name = nam,						\
 		.print_fn = fn, 					\
 		.size = sz,						\
 	} ;								\
         static void logpage_reg_##unique(void) __attribute__((constructor)); \
         static void logpage_reg_##unique(void) { logpage_register(&unique##_lpf); }
 
 #define DEFAULT_SIZE	(4096)
 struct kv_name {
 	uint32_t key;
 	const char *name;
 };
 
 /*
  * Generically convert little endian to host endian, based on the type of the thing
  * being converted. Use the proposed name for future changes to endian.h.
  */
 #define letoh(x)							\
 	_Generic(x,							\
 	uint8_t: (x),							\
 	uint16_t: le16toh(x),						\
 	uint32_t: le32toh(x),						\
 	uint64_t: le64toh(x))
 
 const char *kv_lookup(const struct kv_name *kv, size_t kv_count, uint32_t key);
 
 void logpage_register(struct logpage_function *p);
 #define NVME_CTRLR_PREFIX	"nvme"
 #define NVME_NS_PREFIX		"ns"
 
 int open_dev(const char *str, int *fd, int write, int exit_on_error);
 void get_nsid(int fd, char **ctrlr_str, uint32_t *nsid);
 int read_controller_data(int fd, struct nvme_controller_data *cdata);
 int read_namespace_data(int fd, uint32_t nsid, struct nvme_namespace_data *nsdata);
 void print_hex(void *data, uint32_t length);
 void print_namespace(struct nvme_namespace_data *nsdata);
 void read_logpage(int fd, uint8_t log_page, uint32_t nsid, uint8_t lsp,
     uint16_t lsi, uint8_t rae, void *payload, uint32_t payload_size);
 void print_temp_C(uint16_t t);
 void print_temp_K(uint16_t t);
 void print_intel_add_smart(const struct nvme_controller_data *cdata __unused, void *buf, uint32_t size __unused);
 
 /* Utility Routines */
 /*
- * 128-bit integer augments to standard values. On i386 this
- * doesn't exist, so we use 64-bit values. So, on 32-bit systems,
- * you'll get truncated values until someone implement 128bit
- * ints in software.
+ * C23 supports 128-bit integers via _BitInt(128). clang 16 and gcc 13 support
+ * this. Older compilers will support 128-bit ints on 64-bit
+ * platforms. Otherwise we truncate this to 64-bit on 32-bit systems with older
+ * compilers. We also check for > C18 instead of >= C23 because clang 17 was
+ * released before the the __STDC_VERSION__ was defined.
  */
 #define UINT128_DIG	39
-#ifdef __ILP32__
-typedef uint64_t uint128_t;
-#else
+#if __STDC_VERSION__ >= 202311L
+typedef unsigned _BitInt(128) uint128_t;
+#elif defined(__SIZEOF_INT128__)
 typedef __uint128_t uint128_t;
+#else
+typedef uint64_t uint128_t;
 #endif
 
 static __inline uint128_t
 to128(void *p)
 {
-	return *(uint128_t *)p;
+#if __STDC_VERSION__ >= 202311L || defined(__SIZEOF_INT128__)
+	uint64_t lo, hi;
+
+	lo = le64dec(p);
+	hi = le64dec((const char *)p + 8);
+	return ((uint128_t)hi << 64 | lo);
+#else
+	return (le64dec(p));
+#endif
 }
 
 uint64_t le48dec(const void *pp);
 char * uint128_to_str(uint128_t u, char *buf, size_t buflen);
 #endif