diff --git a/sys/dev/acpica/acpi.c b/sys/dev/acpica/acpi.c
--- a/sys/dev/acpica/acpi.c
+++ b/sys/dev/acpica/acpi.c
@@ -629,9 +629,9 @@
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "sleep_delay", CTLFLAG_RW, &sc->acpi_sleep_delay, 0,
 	"sleep delay in seconds");
-    SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
+    SYSCTL_ADD_BOOL(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "s4bios", CTLFLAG_RW, &sc->acpi_s4bios, 0,
-	"Use S4BIOS when hibernating.");
+	"When hibernating, have the firmware save the machine state (S4BIOS).");
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
 	OID_AUTO, "verbose", CTLFLAG_RW, &sc->acpi_verbose, 0, "verbose mode");
     SYSCTL_ADD_INT(&sc->acpi_sysctl_ctx, SYSCTL_CHILDREN(sc->acpi_sysctl_tree),
@@ -673,7 +673,7 @@
 
     /* Only enable S4BIOS by default if the FACS says it is available. */
     if (AcpiGbl_FACS != NULL && AcpiGbl_FACS->Flags & ACPI_FACS_S4_BIOS_PRESENT)
-	sc->acpi_s4bios = 1;
+	sc->acpi_s4bios = true;
 
     /*
      * Probe all supported ACPI sleep states.  Awake (S0) is always supported.
diff --git a/sys/dev/acpica/acpivar.h b/sys/dev/acpica/acpivar.h
--- a/sys/dev/acpica/acpivar.h
+++ b/sys/dev/acpica/acpivar.h
@@ -64,7 +64,7 @@
     enum power_stype	acpi_lid_switch_stype;
 
     int			acpi_standby_sx;
-    int			acpi_s4bios;
+    bool		acpi_s4bios;
 
     int			acpi_sleep_delay;
     int			acpi_do_disable;