diff --git a/boards/avsextrem/drivers/avsextrem-smb380.c b/boards/avsextrem/drivers/avsextrem-smb380.c
index 3b75e4a562..f1355da8a2 100644
--- a/boards/avsextrem/drivers/avsextrem-smb380.c
+++ b/boards/avsextrem/drivers/avsextrem-smb380.c
@@ -52,7 +52,7 @@ volatile int16_t *ringBuff_Y = NULL;
 volatile int16_t *ringBuff_Z = NULL;
 volatile int16_t *ringBuff_T = NULL;
 uint16_t readPointerPos[SMB380_RING_BUFF_MAX_THREADS];
-u_char PointerList[SMB380_RING_BUFF_MAX_THREADS];
+kernel_pid_t PointerList[SMB380_RING_BUFF_MAX_THREADS];
 static msg_t wakeupmessage;
 
 /*
diff --git a/cpu/cortex-m0_common/thread_arch.c b/cpu/cortex-m0_common/thread_arch.c
index 23ee2a6bcd..d5c7632d56 100644
--- a/cpu/cortex-m0_common/thread_arch.c
+++ b/cpu/cortex-m0_common/thread_arch.c
@@ -122,7 +122,7 @@ void thread_arch_stack_print(void)
     int count = 0;
     uint32_t *sp = (uint32_t *)sched_active_thread->sp;
 
-    printf("printing the current stack of thread %u\n", thread_getpid());
+    printf("printing the current stack of thread %" PRIkernel_pid "\n", thread_getpid());
     printf("  address:      data:\n");
 
     do {
diff --git a/cpu/cortex-m4_common/thread_arch.c b/cpu/cortex-m4_common/thread_arch.c
index da7017233d..7fa0bd4aa4 100644
--- a/cpu/cortex-m4_common/thread_arch.c
+++ b/cpu/cortex-m4_common/thread_arch.c
@@ -127,7 +127,7 @@ void thread_arch_stack_print(void)
     int count = 0;
     uint32_t *sp = (uint32_t *)sched_active_thread->sp;
 
-    printf("printing the current stack of thread %i\n", thread_getpid());
+    printf("printing the current stack of thread %" PRIkernel_pid "\n", thread_getpid());
     printf("  address:      data:\n");
 
     do {
diff --git a/cpu/x86/x86_hwtimer.c b/cpu/x86/x86_hwtimer.c
index c7bd330d9c..b222d200c3 100644
--- a/cpu/x86/x86_hwtimer.c
+++ b/cpu/x86/x86_hwtimer.c
@@ -167,7 +167,7 @@ void x86_init_hwtimer(void)
 static void (*hwtimer_callback)(int timer);
 
 static char hwtimer_stack[KERNEL_CONF_STACKSIZE_DEFAULT];
-static int hwtimer_pid = -1;
+static kernel_pid_t hwtimer_pid = KERNEL_PID_UNDEF;
 
 struct alarm_time {
     uint64_t ts_absolute_alarm;
diff --git a/cpu/x86/x86_rtc.c b/cpu/x86/x86_rtc.c
index fbc6b5bb4b..4e3b73ae09 100644
--- a/cpu/x86/x86_rtc.c
+++ b/cpu/x86/x86_rtc.c
@@ -42,7 +42,7 @@
 static bool valid;
 
 static int32_t alarm_msg_content, periodic_msg_content, update_msg_content;
-static unsigned alarm_pid = KERNEL_PID_UNDEF, periodic_pid = KERNEL_PID_UNDEF, update_pid = KERNEL_PID_UNDEF;
+static kernel_pid_t alarm_pid = KERNEL_PID_UNDEF, periodic_pid = KERNEL_PID_UNDEF, update_pid = KERNEL_PID_UNDEF;
 
 static void alarm_callback_default(uint8_t reg_c)
 {
diff --git a/examples/ccn-lite-client/main.c b/examples/ccn-lite-client/main.c
index f0c3b683d9..59502a6edc 100644
--- a/examples/ccn-lite-client/main.c
+++ b/examples/ccn-lite-client/main.c
@@ -142,7 +142,7 @@ static void riot_ccn_relay_config(int argc, char **argv)
     msg_send(&m, _relay_pid, 1);
 }
 
-static void riot_ccn_transceiver_start(int _relay_pid)
+static void riot_ccn_transceiver_start(kernel_pid_t _relay_pid)
 {
     transceiver_init(TRANSCEIVER);
     int transceiver_pid = transceiver_start();
diff --git a/sys/net/ccn_lite/ccnl-riot-compat.c b/sys/net/ccn_lite/ccnl-riot-compat.c
index c4b560595b..2d38c3ab23 100644
--- a/sys/net/ccn_lite/ccnl-riot-compat.c
+++ b/sys/net/ccn_lite/ccnl-riot-compat.c
@@ -95,7 +95,7 @@ void riot_send_nack(uint16_t to)
 
 void *ccnl_riot_relay_helper_start(void *);
 
-int riot_start_helper_thread(void)
+kernel_pid_t riot_start_helper_thread(void)
 {
     return thread_create(relay_helper_stack, sizeof(relay_helper_stack),
                          PRIORITY_MAIN - 2, CREATE_STACKTEST,
diff --git a/sys/net/ccn_lite/ccnl-riot-compat.h b/sys/net/ccn_lite/ccnl-riot-compat.h
index 223b17cd1c..85076a412b 100644
--- a/sys/net/ccn_lite/ccnl-riot-compat.h
+++ b/sys/net/ccn_lite/ccnl-riot-compat.h
@@ -30,5 +30,5 @@ typedef struct riot_ccnl_msg {
 int riot_send_transceiver(uint8_t *buf, uint16_t size, uint16_t to);
 int riot_send_msg(uint8_t *buf, uint16_t size, uint16_t to);
 void riot_send_nack(uint16_t to);
-int riot_start_helper_thread(void);
+kernel_pid_t riot_start_helper_thread(void);
 char *riot_ccnl_event_to_string(int event);
diff --git a/sys/net/network_layer/sixlowpan/border/border.c b/sys/net/network_layer/sixlowpan/border/border.c
index 5af44877fb..f76138f1a3 100644
--- a/sys/net/network_layer/sixlowpan/border/border.c
+++ b/sys/net/network_layer/sixlowpan/border/border.c
@@ -76,7 +76,7 @@ kernel_pid_t border_get_serial_reader()
 
 void serial_reader_f(void)
 {
-    kernel_pid_t main_pid = KERNEL_PID_UNDEF;
+    kernel_pid_t main_pid;
     int bytes;
     msg_t m;
     border_packet_t *uart_buf;
diff --git a/sys/net/network_layer/sixlowpan/border/border.h b/sys/net/network_layer/sixlowpan/border/border.h
index fbdfe95be5..d64ebcfbfb 100644
--- a/sys/net/network_layer/sixlowpan/border/border.h
+++ b/sys/net/network_layer/sixlowpan/border/border.h
@@ -31,7 +31,7 @@
 
 extern ipv6_addr_t *abr_addr;
 
-uint16_t border_get_serial_reader(void);
+kernel_pid_t border_get_serial_reader(void);
 
 uint8_t *get_serial_out_buffer(int offset);
 uint8_t *get_serial_in_buffer(int offset);
diff --git a/sys/net/network_layer/sixlowpan/ip.c b/sys/net/network_layer/sixlowpan/ip.c
index 4e67571991..64e7c431a2 100644
--- a/sys/net/network_layer/sixlowpan/ip.c
+++ b/sys/net/network_layer/sixlowpan/ip.c
@@ -65,7 +65,7 @@ static uint8_t ipv6_net_if_addr_buffer_count = 0;
 static uint8_t default_hop_limit = MULTIHOP_HOPLIMIT;
 
 /* registered upper layer threads */
-int sixlowip_reg[SIXLOWIP_MAX_REGISTERED];
+kernel_pid_t sixlowip_reg[SIXLOWIP_MAX_REGISTERED];
 
 int ipv6_send_packet(ipv6_hdr_t *packet)
 {
diff --git a/sys/net/network_layer/sixlowpan/ip.h b/sys/net/network_layer/sixlowpan/ip.h
index 3f10cd6bd4..74e5154bcd 100644
--- a/sys/net/network_layer/sixlowpan/ip.h
+++ b/sys/net/network_layer/sixlowpan/ip.h
@@ -58,7 +58,7 @@ extern kernel_pid_t ip_process_pid;
 extern uint8_t buffer[BUFFER_SIZE];
 extern char ip_process_buf[IP_PROCESS_STACKSIZE];
 
-extern int sixlowip_reg[SIXLOWIP_MAX_REGISTERED];
+extern kernel_pid_t sixlowip_reg[SIXLOWIP_MAX_REGISTERED];
 
 typedef struct __attribute__((packed)) {
     struct net_if_addr_t *addr_next;
diff --git a/sys/net/network_layer/sixlowpan/lowpan.c b/sys/net/network_layer/sixlowpan/lowpan.c
index 9d9994bb0b..8fd7bf74bd 100644
--- a/sys/net/network_layer/sixlowpan/lowpan.c
+++ b/sys/net/network_layer/sixlowpan/lowpan.c
@@ -131,7 +131,7 @@ kernel_pid_t transfer_pid = KERNEL_PID_UNDEF;
 mutex_t lowpan_context_mutex = MUTEX_INIT;
 
 /* registered upper layer threads */
-int sixlowpan_reg[SIXLOWPAN_MAX_REGISTERED];
+kernel_pid_t sixlowpan_reg[SIXLOWPAN_MAX_REGISTERED];
 static sixlowpan_lowpan_frame_t current_frame;
 
 char ip_process_buf[IP_PROCESS_STACKSIZE];
diff --git a/sys/net/transport_layer/destiny/socket.h b/sys/net/transport_layer/destiny/socket.h
index f80cffd745..1da09c04af 100644
--- a/sys/net/transport_layer/destiny/socket.h
+++ b/sys/net/transport_layer/destiny/socket.h
@@ -61,8 +61,8 @@ typedef struct __attribute__((packed)) {
 
 typedef struct {
     uint8_t             socket_id;
-    uint8_t             recv_pid;
-    uint8_t             send_pid;
+    kernel_pid_t        recv_pid;
+    kernel_pid_t        send_pid;
     uint8_t             tcp_input_buffer_end;
     mutex_t             tcp_buffer_mutex;
     socket_t            socket_values;
diff --git a/sys/posix/pthread/pthread.c b/sys/posix/pthread/pthread.c
index 4ba1825d4d..d657f8ba0d 100644
--- a/sys/posix/pthread/pthread.c
+++ b/sys/posix/pthread/pthread.c
@@ -57,7 +57,7 @@ typedef struct pthread_thread {
     kernel_pid_t thread_pid;
 
     enum pthread_thread_status status;
-    int joining_thread;
+    kernel_pid_t joining_thread;
     void *returnval;
     bool should_cancel;
 
@@ -72,7 +72,7 @@ typedef struct pthread_thread {
 static pthread_thread_t *volatile pthread_sched_threads[MAXTHREADS];
 static struct mutex_t pthread_mutex;
 
-static volatile int pthread_reaper_pid = KERNEL_PID_UNDEF;
+static volatile kernel_pid_t pthread_reaper_pid = KERNEL_PID_UNDEF;
 
 static char pthread_reaper_stack[PTHREAD_REAPER_STACKSIZE];
 
diff --git a/tests/thread_msg/main.c b/tests/thread_msg/main.c
index bebd5eab72..8cdef7d725 100644
--- a/tests/thread_msg/main.c
+++ b/tests/thread_msg/main.c
@@ -28,7 +28,7 @@ char t1_stack[KERNEL_CONF_STACKSIZE_MAIN];
 char t2_stack[KERNEL_CONF_STACKSIZE_MAIN];
 char t3_stack[KERNEL_CONF_STACKSIZE_MAIN];
 
-uint16_t p1, p2, p3;
+kernel_pid_t p1, p2, p3;
 
 void *thread1(void *arg)
 {
diff --git a/tests/unittests/tests-lib/tests-lib-ringbuffer.c b/tests/unittests/tests-lib/tests-lib-ringbuffer.c
index b4a42e28da..bf6458e75d 100644
--- a/tests/unittests/tests-lib/tests-lib-ringbuffer.c
+++ b/tests/unittests/tests-lib/tests-lib-ringbuffer.c
@@ -33,7 +33,7 @@ static char stack_get[KERNEL_CONF_STACKSIZE_DEFAULT];
 static char rb_buf[BUF_SIZE];
 static ringbuffer_t rb = RINGBUFFER_INIT(rb_buf);
 static mutex_t mutex;
-static unsigned pid_add, pid_get;
+static kernel_pid_t pid_add, pid_get;
 
 static void assert_avail(unsigned assumed)
 {