diff --git a/sys/contrib/dev/acpica/dmresrc.c b/sys/contrib/dev/acpica/dmresrc.c
index 0fb4cb5d6840..fe1d81bb1b22 100644
--- a/sys/contrib/dev/acpica/dmresrc.c
+++ b/sys/contrib/dev/acpica/dmresrc.c
@@ -435,7 +435,7 @@ AcpiDmIsResourceDescriptor (
 
     /* The list must have a valid END_TAG */
 
-    if (ByteData[ByteCount-2] != (ACPI_RDESC_TYPE_END_TAG | 1))
+    if (ByteData[ByteCount-1] != (ACPI_RDESC_TYPE_END_TAG | 1))
     {
         return FALSE;
     }