diff --git a/include/acpi/actypes.h b/include/acpi/actypes.h
index ce1db1c2e9d3..cf6ee2cb0eb9 100644
--- a/include/acpi/actypes.h
+++ b/include/acpi/actypes.h
@@ -1323,4 +1323,8 @@ typedef enum {
 #define ACPI_FALLTHROUGH do {} while(0)
 #endif
 
+#ifndef ACPI_FLEX_ARRAY
+#define ACPI_FLEX_ARRAY(TYPE, NAME)     TYPE NAME[0]
+#endif
+
 #endif				/* __ACTYPES_H__ */
diff --git a/include/acpi/platform/acgcc.h b/include/acpi/platform/acgcc.h
index c9d418f9395e..04b4bf620517 100644
--- a/include/acpi/platform/acgcc.h
+++ b/include/acpi/platform/acgcc.h
@@ -61,4 +61,15 @@
 #define ACPI_FALLTHROUGH __attribute__((__fallthrough__))
 #endif
 
+/*
+ * Flexible array members are not allowed to be part of a union under
+ * C99, but this is not for any technical reason. Work around the
+ * limitation.
+ */
+#define ACPI_FLEX_ARRAY(TYPE, NAME)             \
+        struct {                                \
+                struct { } __Empty_ ## NAME;    \
+                TYPE NAME[];                    \
+        }
+
 #endif				/* __ACGCC_H__ */