diff --git a/sys/arm64/acpica/OsdEnvironment.c b/sys/arm64/acpica/OsdEnvironment.c
--- a/sys/arm64/acpica/OsdEnvironment.c
+++ b/sys/arm64/acpica/OsdEnvironment.c
@@ -60,6 +60,16 @@
 {
 	long acpi_root;
 
+	if (TUNABLE_ULONG_FETCH("acpi.rsdp", &acpi_root))
+		return (acpi_root);
+
+	/*
+	 * The hints mechanism is unreliable (it fails if anybody ever
+	 * compiled in hints to the kernel). It has been replaced
+	 * by the tunable method, but is used here as a fallback to
+	 * retain maximum compatibility between old loaders and new
+	 * kernels. It can be removed after 14.0R.
+	 */
 	if (resource_long_value("acpi", 0, "rsdp", &acpi_root) == 0)
 		return (acpi_root);