diff --git a/source/tools/acpiexec/aehandlers.c b/source/tools/acpiexec/aehandlers.c
index 0ee6dd94b..6c0d245fc 100644
--- a/source/tools/acpiexec/aehandlers.c
+++ b/source/tools/acpiexec/aehandlers.c
@@ -172,29 +172,32 @@ static AE_DEBUG_REGIONS     AeRegions;
 
 
 /*
- * We will override default region handlers for memory and I/O. Especially
- * the SystemMemory handler, which must be implemented locally to simulate
- * memory operation regions. Do not override the PCI_Config handler since
- * we would like to exercise the default handler code. Do not override
- * DataTable handler, since the default handler works correctly under
- * acpiexec (and is used by the test suites.)
+ * We will override some of the default region handlers, especially the
+ * SystemMemory handler, which must be implemented locally. Do not override
+ * the PCI_Config handler since we would like to exercise the default handler
+ * code. These handlers are installed "early" - before any _REG methods
+ * are executed - since they are special in the sense that tha ACPI spec
+ * declares that they must "always be available". Cannot override the
+ * DataTable region handler either -- needed for test execution.
  */
-static ACPI_ADR_SPACE_TYPE  DefaultSpaceIdList[] =
-{
+static ACPI_ADR_SPACE_TYPE  DefaultSpaceIdList[] = {
     ACPI_ADR_SPACE_SYSTEM_MEMORY,
     ACPI_ADR_SPACE_SYSTEM_IO
 };
 
 /*
  * We will install handlers for some of the various address space IDs
+ * Test one user-defined address space (used by aslts.)
  */
-static ACPI_ADR_SPACE_TYPE  SpaceIdList[] =
-{
+#define ACPI_ADR_SPACE_USER_DEFINED     0x80
+
+static ACPI_ADR_SPACE_TYPE  SpaceIdList[] = {
     ACPI_ADR_SPACE_EC,
     ACPI_ADR_SPACE_SMBUS,
     ACPI_ADR_SPACE_PCI_BAR_TARGET,
     ACPI_ADR_SPACE_IPMI,
-    ACPI_ADR_SPACE_FIXED_HARDWARE
+    ACPI_ADR_SPACE_FIXED_HARDWARE,
+    ACPI_ADR_SPACE_USER_DEFINED
 };