diff --git a/include/lib/libc/stddef.h b/include/lib/libc/stddef.h
index c9957bd..58a519e 100644
--- a/include/lib/libc/stddef.h
+++ b/include/lib/libc/stddef.h
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 /*
- * Portions copyright (c) 2018, ARM Limited and Contributors.
+ * Portions copyright (c) 2018-2019, ARM Limited and Contributors.
  * All rights reserved.
  */
 
@@ -13,6 +13,11 @@
 
 #include <stddef_.h>
 
+#ifndef _PTRDIFF_T
+typedef long ptrdiff_t;
+#define _PTRDIFF_T
+#endif
+
 #ifndef NULL
 #define NULL ((void *) 0)
 #endif