diff --git a/include/lib/libc/aarch32/stdio_.h b/include/lib/libc/aarch32/stdio_.h
index 50d3cc2..5e49425 100644
--- a/include/lib/libc/aarch32/stdio_.h
+++ b/include/lib/libc/aarch32/stdio_.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,11 +7,6 @@
 #ifndef STDIO__H
 #define STDIO__H
 
-#ifndef SIZET_
-typedef unsigned int size_t;
-#define SIZET_
-#endif
-
 #ifndef SSIZET_
 typedef int ssize_t;
 #define SSIZET_
diff --git a/include/lib/libc/aarch32/stdlib_.h b/include/lib/libc/aarch32/stdlib_.h
deleted file mode 100644
index ff53b6f..0000000
--- a/include/lib/libc/aarch32/stdlib_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef STDLIB__H
-#define STDLIB__H
-
-#ifndef SIZET_
-typedef unsigned int size_t;
-#define SIZET_
-#endif
-
-#endif /* STDLIB__H */
diff --git a/include/lib/libc/aarch32/string_.h b/include/lib/libc/aarch32/string_.h
deleted file mode 100644
index 4e139b0..0000000
--- a/include/lib/libc/aarch32/string_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef STRING__H
-#define STRING__H
-
-#ifndef SIZET_
-typedef unsigned int size_t;
-#define SIZET_
-#endif
-
-#endif /* STRING__H */
diff --git a/include/lib/libc/aarch32/time_.h b/include/lib/libc/aarch32/time_.h
deleted file mode 100644
index cfd487d..0000000
--- a/include/lib/libc/aarch32/time_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef TIME__H
-#define TIME__H
-
-#ifndef SIZET_
-typedef unsigned int size_t;
-#define SIZET_
-#endif
-
-#endif /* TIME__H */
diff --git a/include/lib/libc/aarch64/stdio_.h b/include/lib/libc/aarch64/stdio_.h
index 09b0172..afaeadc 100644
--- a/include/lib/libc/aarch64/stdio_.h
+++ b/include/lib/libc/aarch64/stdio_.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,11 +7,6 @@
 #ifndef STDIO__H
 #define STDIO__H
 
-#ifndef SIZET_
-typedef unsigned long size_t;
-#define SIZET_
-#endif
-
 #ifndef SSIZET_
 typedef long ssize_t;
 #define SSIZET_
diff --git a/include/lib/libc/aarch64/stdlib_.h b/include/lib/libc/aarch64/stdlib_.h
deleted file mode 100644
index 531308a..0000000
--- a/include/lib/libc/aarch64/stdlib_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef STDLIB__H
-#define STDLIB__H
-
-#ifndef SIZET_
-typedef unsigned long size_t;
-#define SIZET_
-#endif
-
-#endif /* STDLIB__H */
diff --git a/include/lib/libc/aarch64/string_.h b/include/lib/libc/aarch64/string_.h
deleted file mode 100644
index 71c51a6..0000000
--- a/include/lib/libc/aarch64/string_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef STRING__H
-#define STRING__H
-
-#ifndef SIZET_
-typedef unsigned long size_t;
-#define SIZET_
-#endif
-
-#endif /* STRING__H */
diff --git a/include/lib/libc/aarch64/time_.h b/include/lib/libc/aarch64/time_.h
deleted file mode 100644
index 8b298a3..0000000
--- a/include/lib/libc/aarch64/time_.h
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#ifndef TIME__H
-#define TIME__H
-
-#ifndef SIZET_
-typedef unsigned long size_t;
-#define SIZET_
-#endif
-
-#endif /* TIME__H */
diff --git a/include/lib/libc/stdio.h b/include/lib/libc/stdio.h
index 3d9323e..2d9e655 100644
--- a/include/lib/libc/stdio.h
+++ b/include/lib/libc/stdio.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.
  */
 
@@ -12,12 +12,9 @@
 #define STDIO_H
 
 #include <cdefs.h>
+#include <stddef.h>
 #include <stdio_.h>
 
-#ifndef NULL
-#define NULL ((void *) 0)
-#endif
-
 #define EOF            -1
 
 int printf(const char *fmt, ...) __printflike(1, 2);
diff --git a/include/lib/libc/stdlib.h b/include/lib/libc/stdlib.h
index 84ba37f..24e7bae 100644
--- a/include/lib/libc/stdlib.h
+++ b/include/lib/libc/stdlib.h
@@ -11,15 +11,11 @@
 #ifndef STDLIB_H
 #define STDLIB_H
 
-#include <stdlib_.h>
+#include <stddef.h>
 
 #define EXIT_FAILURE 1
 #define EXIT_SUCCESS 0
 
-#ifndef NULL
-#define NULL ((void *) 0)
-#endif
-
 #define _ATEXIT_MAX 1
 
 extern void abort(void);
diff --git a/include/lib/libc/string.h b/include/lib/libc/string.h
index ee6eeac..c92b680 100644
--- a/include/lib/libc/string.h
+++ b/include/lib/libc/string.h
@@ -4,18 +4,14 @@
  * 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.
  */
 
 #ifndef STRING_H
 #define STRING_H
 
-#include <string_.h>
-
-#ifndef NULL
-#define NULL ((void *) 0)
-#endif
+#include <stddef.h>
 
 void *memcpy(void *dst, const void *src, size_t len);
 void *memmove(void *dst, const void *src, size_t len);
diff --git a/include/lib/libc/time.h b/include/lib/libc/time.h
index 714884b..c1c95e5 100644
--- a/include/lib/libc/time.h
+++ b/include/lib/libc/time.h
@@ -11,12 +11,8 @@
 #ifndef TIME_H
 #define TIME_H
 
-#include <time_.h>
+#include <stddef.h>
 
 typedef long int time_t;
 
-#ifndef NULL
-#define NULL ((void *) 0)
-#endif
-
 #endif /* TIME_H */