diff --git a/share/man/man4/acpi.4 b/share/man/man4/acpi.4
index b8198af4c5a0..950ab820b853 100644
--- a/share/man/man4/acpi.4
+++ b/share/man/man4/acpi.4
@@ -99,6 +99,11 @@ Enables loading of a custom ACPI DSDT.
 Name of the DSDT table to load, if loading is enabled.
 .It Va debug.acpi.disabled
 Selectively disables portions of ACPI for debugging purposes.
+.It Va debug.acpi.max_threads
+Specify the number of task threads that are started on boot.
+Limiting this to 1 may help work around various BIOSes that cannot
+handle parallel requests.
+The default value is 3.
 .It Va debug.acpi.quirks
 Override any automatic quirks completely.
 .It Va hint.acpi.0.disabled