diff --git a/kernel/atomkernel.c b/kernel/atomkernel.c
index 4b53af1..9c0e276 100755
--- a/kernel/atomkernel.c
+++ b/kernel/atomkernel.c
@@ -143,12 +143,6 @@
  *
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <atom-types.h>
-#include <printk.h>
-#endif
 
 #include "atom.h"
 
diff --git a/kernel/atomport-template.h b/kernel/atomport-template.h
index 07671ea..4f47cb4 100755
--- a/kernel/atomport-template.h
+++ b/kernel/atomport-template.h
@@ -34,6 +34,12 @@
 /* Required number of system ticks per second (normally 100 for 10ms tick) */
 #define SYSTEM_TICKS_PER_SEC            100
 
+/**
+ * Definition of NULL.
+ * If stddef.h is available on the platform it is simplest to include it
+ * from this header, otherwise define below.
+ */
+#define NULL      ((void *)(0))
 
 /**
  * Architecture-specific types.
diff --git a/ports/avr/atomport.h b/ports/avr/atomport.h
index ec1cc78..094e17e 100644
--- a/ports/avr/atomport.h
+++ b/ports/avr/atomport.h
@@ -37,6 +37,8 @@
 /* Portable uint8_t and friends available from stdint.h on this platform */
 #include <stdint.h>
 
+/* Definition of NULL is available from stddef.h on this platform */
+#include <stddef.h>
 
 /* Required number of system ticks per second (normally 100 for 10ms tick) */
 #define SYSTEM_TICKS_PER_SEC            100
diff --git a/ports/stm8/atomport.h b/ports/stm8/atomport.h
index 119c2b5..bcd36e1 100644
--- a/ports/stm8/atomport.h
+++ b/ports/stm8/atomport.h
@@ -39,6 +39,8 @@
 #include <intrins.h>
 #endif
 
+/* Definition of NULL is available from stddef.h on this platform */
+#include <stddef.h>
 
 /* Required number of system ticks per second (normally 100 for 10ms tick) */
 #define SYSTEM_TICKS_PER_SEC            100
diff --git a/ports/stm8/uart.c b/ports/stm8/uart.c
index 352ea13..90515ac 100644
--- a/ports/stm8/uart.c
+++ b/ports/stm8/uart.c
@@ -1,5 +1,4 @@
 #include <stdio.h>
-#include <stddef.h>
 
 #include "stm8s.h"
 
diff --git a/tests/kern1.c b/tests/kern1.c
index c467298..90a3991 100644
--- a/tests/kern1.c
+++ b/tests/kern1.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomtests.h"
diff --git a/tests/mutex1.c b/tests/mutex1.c
index a2b03e7..4a340d2 100644
--- a/tests/mutex1.c
+++ b/tests/mutex1.c
@@ -27,13 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
-
 #include "atom.h"
 #include "atommutex.h"
 #include "atomtests.h"
diff --git a/tests/mutex2.c b/tests/mutex2.c
index 7e90d22..5432ec3 100644
--- a/tests/mutex2.c
+++ b/tests/mutex2.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atommutex.h"
diff --git a/tests/mutex7.c b/tests/mutex7.c
index e9edcb6..7d25fae 100644
--- a/tests/mutex7.c
+++ b/tests/mutex7.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomtests.h"
diff --git a/tests/queue1.c b/tests/queue1.c
index 50089c6..8b50f91 100644
--- a/tests/queue1.c
+++ b/tests/queue1.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomqueue.h"
diff --git a/tests/queue4.c b/tests/queue4.c
index 46703d4..e5c5d94 100644
--- a/tests/queue4.c
+++ b/tests/queue4.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomqueue.h"
diff --git a/tests/sem1.c b/tests/sem1.c
index 69623eb..54b7ddc 100644
--- a/tests/sem1.c
+++ b/tests/sem1.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomsem.h"
diff --git a/tests/sem2.c b/tests/sem2.c
index d7f0e40..f025e50 100644
--- a/tests/sem2.c
+++ b/tests/sem2.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomsem.h"
diff --git a/tests/timer1.c b/tests/timer1.c
index d1bbf39..6cc57d9 100644
--- a/tests/timer1.c
+++ b/tests/timer1.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomsem.h"
diff --git a/tests/timer3.c b/tests/timer3.c
index e6f9104..be81c14 100644
--- a/tests/timer3.c
+++ b/tests/timer3.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomsem.h"
diff --git a/tests/timer5.c b/tests/timer5.c
index acf56b1..080a5b8 100644
--- a/tests/timer5.c
+++ b/tests/timer5.c
@@ -27,12 +27,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef STAND_ALONE
-#include <stddef.h>
-#else
-#include <printk.h>
-#include <atom-types.h>
-#endif
 
 #include "atom.h"
 #include "atomsem.h"