diff --git a/include/hw/xen/interface/physdev.h b/include/hw/xen/interface/physdev.h
index f0c0d4727c..ca2bcbfd15 100644
--- a/include/hw/xen/interface/physdev.h
+++ b/include/hw/xen/interface/physdev.h
@@ -283,7 +283,7 @@ struct physdev_pci_device_add {
      * First element ([0]) is PXM domain associated with the device (if
      * XEN_PCI_DEV_PXM is set)
      */
-    uint32_t optarr[XEN_FLEX_ARRAY_DIM];
+    uint32_t optarr[];
 };
 typedef struct physdev_pci_device_add physdev_pci_device_add_t;
 DEFINE_XEN_GUEST_HANDLE(physdev_pci_device_add_t);
diff --git a/include/hw/xen/interface/version.h b/include/hw/xen/interface/version.h
index 9c78b4f3b6..2f183c3efd 100644
--- a/include/hw/xen/interface/version.h
+++ b/include/hw/xen/interface/version.h
@@ -77,9 +77,8 @@ typedef char xen_commandline_t[1024];
  */
 #define XENVER_build_id 10
 struct xen_build_id {
-        uint32_t        len; /* IN: size of buf[]. */
-        unsigned char   buf[XEN_FLEX_ARRAY_DIM];
-                             /* OUT: Variable length buffer with build_id. */
+        uint32_t        len;    /* IN: size of buf[]. */
+        unsigned char   buf[];  /* OUT: Variable length buffer with build_id. */
 };
 typedef struct xen_build_id xen_build_id_t;
 
diff --git a/include/hw/xen/interface/xen-compat.h b/include/hw/xen/interface/xen-compat.h
index 97fe698498..582c018236 100644
--- a/include/hw/xen/interface/xen-compat.h
+++ b/include/hw/xen/interface/xen-compat.h
@@ -24,6 +24,4 @@
 #error "These header files do not support the requested interface version."
 #endif
 
-#define COMPAT_FLEX_ARRAY_DIM XEN_FLEX_ARRAY_DIM
-
 #endif /* __XEN_PUBLIC_XEN_COMPAT_H__ */
diff --git a/include/hw/xen/interface/xen.h b/include/hw/xen/interface/xen.h
index 920567e006..a6f4aa6199 100644
--- a/include/hw/xen/interface/xen.h
+++ b/include/hw/xen/interface/xen.h
@@ -36,15 +36,6 @@ DEFINE_XEN_GUEST_HANDLE(uint64_t);
 DEFINE_XEN_GUEST_HANDLE(xen_pfn_t);
 DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
 
-/* Define a variable length array (depends on compiler). */
-#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
-#define XEN_FLEX_ARRAY_DIM
-#elif defined(__GNUC__)
-#define XEN_FLEX_ARRAY_DIM  0
-#else
-#define XEN_FLEX_ARRAY_DIM  1 /* variable size */
-#endif
-
 /* Turn a plain number into a C unsigned (long (long)) constant. */
 #define __xen_mk_uint(x)  x ## U
 #define __xen_mk_ulong(x) x ## UL
@@ -986,13 +977,8 @@ typedef struct {
       ((d) >>  8) & 0xFF, ((d) >>  0) & 0xFF,                           \
                 e1, e2, e3, e4, e5, e6}}
 
-#if defined(__STDC_VERSION__) ? __STDC_VERSION__ >= 199901L : defined(__GNUC__)
 #define XEN_DEFINE_UUID(a, b, c, d, e1, e2, e3, e4, e5, e6)             \
     ((xen_uuid_t)XEN_DEFINE_UUID_(a, b, c, d, e1, e2, e3, e4, e5, e6))
-#else
-#define XEN_DEFINE_UUID(a, b, c, d, e1, e2, e3, e4, e5, e6)             \
-    XEN_DEFINE_UUID_(a, b, c, d, e1, e2, e3, e4, e5, e6)
-#endif /* __STDC_VERSION__ / __GNUC__ */
 
 #endif /* !__ASSEMBLY__ */