diff --git a/include/os/freebsd/spl/sys/misc.h b/include/os/freebsd/spl/sys/misc.h
index 3481507d2c..2e4efc6054 100644
--- a/include/os/freebsd/spl/sys/misc.h
+++ b/include/os/freebsd/spl/sys/misc.h
@@ -52,8 +52,6 @@ struct opensolaris_utsname {
 	char	*machine;
 };
 
-extern char hw_serial[11];
-
 #define	task_io_account_read(n)
 #define	task_io_account_write(n)
 
diff --git a/include/os/freebsd/spl/sys/sunddi.h b/include/os/freebsd/spl/sys/sunddi.h
index bfbc3e10a1..28d40121d9 100644
--- a/include/os/freebsd/spl/sys/sunddi.h
+++ b/include/os/freebsd/spl/sys/sunddi.h
@@ -48,7 +48,6 @@ typedef int ddi_devid_t;
 #define	ddi_prop_free(x)				(void)0
 #define	ddi_root_node()					(void)0
 
-extern int ddi_strtoul(const char *, char **, int, unsigned long *);
 extern int ddi_strtol(const char *, char **, int, long *);
 extern int ddi_strtoull(const char *, char **, int, unsigned long long *);
 extern int ddi_strtoll(const char *, char **, int, long long *);
diff --git a/include/os/linux/spl/sys/sunddi.h b/include/os/linux/spl/sys/sunddi.h
index 8524ec9c30..df6a204d5c 100644
--- a/include/os/linux/spl/sys/sunddi.h
+++ b/include/os/linux/spl/sys/sunddi.h
@@ -46,7 +46,6 @@ typedef int ddi_devid_t;
 #define	ddi_prop_free(x)				(void)0
 #define	ddi_root_node()					(void)0
 
-extern int ddi_strtoul(const char *, char **, int, unsigned long *);
 extern int ddi_strtol(const char *, char **, int, long *);
 extern int ddi_strtoull(const char *, char **, int, unsigned long long *);
 extern int ddi_strtoll(const char *, char **, int, long long *);
diff --git a/include/sys/zfs_context.h b/include/sys/zfs_context.h
index 944acdcfbe..50257f1d6f 100644
--- a/include/sys/zfs_context.h
+++ b/include/sys/zfs_context.h
@@ -692,10 +692,6 @@ extern char *kmem_asprintf(const char *fmt, ...);
 /*
  * Hostname information
  */
-extern char hw_serial[];	/* for userland-emulated hostid access */
-extern int ddi_strtoul(const char *str, char **nptr, int base,
-    unsigned long *result);
-
 extern int ddi_strtoull(const char *str, char **nptr, int base,
     u_longlong_t *result);
 
diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index 89151f70ec..011f9d2110 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -53,7 +53,7 @@
  */
 
 uint64_t physmem;
-char hw_serial[HW_HOSTID_LEN];
+uint32_t hostid;
 struct utsname hw_utsname;
 
 /* If set, all blocks read will be copied to the specified directory. */
@@ -299,7 +299,7 @@ zone_get_hostid(void *zonep)
 	 * We're emulating the system's hostid in userland.
 	 */
 	(void) zonep;
-	return (strtoul(hw_serial, NULL, 10));
+	return (hostid);
 }
 
 int
@@ -766,18 +766,6 @@ random_get_pseudo_bytes(uint8_t *ptr, size_t len)
 	return (random_get_bytes_common(ptr, len, urandom_fd));
 }
 
-int
-ddi_strtoul(const char *hw_serial, char **nptr, int base, unsigned long *result)
-{
-	(void) nptr;
-	char *end;
-
-	*result = strtoul(hw_serial, &end, base);
-	if (*result == 0)
-		return (errno);
-	return (0);
-}
-
 int
 ddi_strtoull(const char *str, char **nptr, int base, u_longlong_t *result)
 {
@@ -823,8 +811,7 @@ kernel_init(int mode)
 	dprintf("physmem = %llu pages (%.2f GB)\n", (u_longlong_t)physmem,
 	    (double)physmem * sysconf(_SC_PAGE_SIZE) / (1ULL << 30));
 
-	(void) snprintf(hw_serial, sizeof (hw_serial), "%ld",
-	    (mode & SPA_MODE_WRITE) ? get_system_hostid() : 0);
+	hostid = (mode & SPA_MODE_WRITE) ? get_system_hostid() : 0;
 
 	random_init();
 
diff --git a/module/os/freebsd/spl/spl_misc.c b/module/os/freebsd/spl/spl_misc.c
index 0354b986cd..e46271a039 100644
--- a/module/os/freebsd/spl/spl_misc.c
+++ b/module/os/freebsd/spl/spl_misc.c
@@ -43,15 +43,11 @@ static struct opensolaris_utsname hw_utsname = {
 	.machine = MACHINE
 };
 
-#ifndef KERNEL_STATIC
-char hw_serial[11] = "0";
-
 utsname_t *
 utsname(void)
 {
 	return (&hw_utsname);
 }
-#endif
 
 static void
 opensolaris_utsname_init(void *arg)
diff --git a/module/os/freebsd/spl/spl_sunddi.c b/module/os/freebsd/spl/spl_sunddi.c
index ebec77bdb3..2a3c027c93 100644
--- a/module/os/freebsd/spl/spl_sunddi.c
+++ b/module/os/freebsd/spl/spl_sunddi.c
@@ -45,19 +45,6 @@ ddi_strtol(const char *str, char **nptr, int base, long *result)
 	return (0);
 }
 
-int
-ddi_strtoul(const char *str, char **nptr, int base, unsigned long *result)
-{
-
-	if (str == hw_serial) {
-		*result = prison0.pr_hostid;
-		return (0);
-	}
-
-	*result = strtoul(str, nptr, base);
-	return (0);
-}
-
 int
 ddi_strtoull(const char *str, char **nptr, int base, unsigned long long *result)
 {
diff --git a/module/os/linux/spl/spl-generic.c b/module/os/linux/spl/spl-generic.c
index 143f345985..6fa564b855 100644
--- a/module/os/linux/spl/spl-generic.c
+++ b/module/os/linux/spl/spl-generic.c
@@ -425,13 +425,13 @@ EXPORT_SYMBOL(__aeabi_ldivmod);
  * functions against their Solaris counterparts.  It is possible that I
  * may have misinterpreted the man page or the man page is incorrect.
  */
-int ddi_strtoul(const char *, char **, int, unsigned long *);
+static int ddi_strtoul(const char *, char **, int, unsigned long *);
 int ddi_strtol(const char *, char **, int, long *);
 int ddi_strtoull(const char *, char **, int, unsigned long long *);
 int ddi_strtoll(const char *, char **, int, long long *);
 
-#define	define_ddi_strtoux(type, valtype)				\
-int ddi_strtou##type(const char *str, char **endptr,			\
+#define	define_ddi_strtoux(type, valtype, ...)				\
+__VA_ARGS__ int ddi_strtou##type(const char *str, char **endptr,	\
     int base, valtype *result)						\
 {									\
 	valtype last_value, value = 0;					\
@@ -508,12 +508,12 @@ int ddi_strto##type(const char *str, char **endptr,			\
 	return (rc);							\
 }
 
-define_ddi_strtoux(l, unsigned long)
+#define	blank
+define_ddi_strtoux(l, unsigned long, static)
 define_ddi_strtox(l, long)
-define_ddi_strtoux(ll, unsigned long long)
+define_ddi_strtoux(ll, unsigned long long, blank)
 define_ddi_strtox(ll, long long)
 
-EXPORT_SYMBOL(ddi_strtoul);
 EXPORT_SYMBOL(ddi_strtol);
 EXPORT_SYMBOL(ddi_strtoll);
 EXPORT_SYMBOL(ddi_strtoull);