diff --git a/boards/avsextrem/drivers/avsextrem-cc1100.c b/boards/avsextrem/drivers/avsextrem-cc1100.c
index 705e087f4b..49237f0706 100644
--- a/boards/avsextrem/drivers/avsextrem-cc1100.c
+++ b/boards/avsextrem/drivers/avsextrem-cc1100.c
@@ -58,7 +58,7 @@ static int test_time(int code)
     time_value++;
 
     if (time_value > 10000000) {
-        printf("CC1100 SPI alarm: %u!\n", code);
+        printf("CC1100 SPI alarm: %d!\n", code);
         time_value = 0;
         return 1;
     }
diff --git a/boards/msba2-common/tools/src/download.c b/boards/msba2-common/tools/src/download.c
index f623e814b1..b25707e93d 100644
--- a/boards/msba2-common/tools/src/download.c
+++ b/boards/msba2-common/tools/src/download.c
@@ -641,7 +641,7 @@ static void download_main(int event)
                             break;
                         }
 
-                        snprintf(buf, sizeof(buf), "W %d %d\r\n", chip->ram_addr, chip->chunk_size);
+                        snprintf(buf, sizeof(buf), "W %u %d\r\n", chip->ram_addr, chip->chunk_size);
                         xmit_cmd(buf, 4);
                         return;
 
@@ -721,7 +721,7 @@ static void download_main(int event)
             case XMIT_CKSUM:
                 switch (event) {
                     case BEGIN:
-                        snprintf(buf, sizeof(buf), "%d\r\n", cksum);
+                        snprintf(buf, sizeof(buf), "%u\r\n", cksum);
                         xmit_cmd(buf, 3);
                         return;
 
@@ -795,7 +795,7 @@ static void download_main(int event)
                     case BEGIN:
                         printf("write, ");
                         fflush(stdout);
-                        snprintf(buf, sizeof(buf), "C %d %d %d\r\n",
+                        snprintf(buf, sizeof(buf), "C %d %u %d\r\n",
                                  chip->layout[sector].address + sector_offset,
                                  chip->ram_addr, chip->chunk_size);
                         xmit_cmd(buf, 5);
@@ -856,7 +856,7 @@ static void download_main(int event)
                         // bootloader again.  Intead, we need to download a tiny ARM
                         // program that reconfigures the hardware and then jumps to zero.
                         //snprintf(buf, sizeof(buf), "G %d A\r\n", 0);
-                        snprintf(buf, sizeof(buf), "W %d %d\r\n", chip->ram_addr, chip->bootprog[0] * 4);
+                        snprintf(buf, sizeof(buf), "W %u %d\r\n", chip->ram_addr, chip->bootprog[0] * 4);
                         xmit_cmd(buf, 4);
                         return;
 
@@ -938,7 +938,7 @@ static void download_main(int event)
             case BOOT_XMIT_CKSUM:
                 switch (event) {
                     case BEGIN:
-                        snprintf(buf, sizeof(buf), "%d\r\n", cksum);
+                        snprintf(buf, sizeof(buf), "%u\r\n", cksum);
                         //printf("send: %s", buf);
                         xmit_cmd(buf, 3);
                         return;
@@ -980,7 +980,7 @@ static void download_main(int event)
                 switch (event) {
                     case BEGIN:
                         printf("jumping now!\r\n");
-                        snprintf(buf, sizeof(buf), "G %d A\r\n", chip->ram_addr);
+                        snprintf(buf, sizeof(buf), "G %u A\r\n", chip->ram_addr);
                         xmit_cmd(buf, 4);
                         return;
 
diff --git a/boards/msba2/msba2-cc110x.c b/boards/msba2/msba2-cc110x.c
index 356c96a9fd..6c9bf97ffe 100644
--- a/boards/msba2/msba2-cc110x.c
+++ b/boards/msba2/msba2-cc110x.c
@@ -57,7 +57,7 @@ static int test_time(int code)
     time_value++;
 
     if (time_value > 10000000) {
-        printf("CC1100 SPI alarm: %u!\n", code);
+        printf("CC1100 SPI alarm: %d!\n", code);
         time_value = 0;
         return 1;
     }
diff --git a/cpu/arm_common/arm_cpu.c b/cpu/arm_common/arm_cpu.c
index a615327c2d..21b4d6c6c9 100644
--- a/cpu/arm_common/arm_cpu.c
+++ b/cpu/arm_common/arm_cpu.c
@@ -78,12 +78,12 @@ void thread_print_stack(void)
     s += 5;
 
     while (*s != STACK_MARKER) {
-        printf("STACK (%u) addr=%X = %X \n", i, (unsigned int) s, (unsigned int) *s);
+        printf("STACK (%d) addr=%X = %X \n", i, (unsigned int) s, (unsigned int) *s);
         s++;
         i++;
     }
 
-    printf("STACK (%u)= %X \n", i, *s);
+    printf("STACK (%d)= %X \n", i, *s);
 }
 
 int reboot_arch(int mode)
diff --git a/cpu/arm_common/syscalls.c b/cpu/arm_common/syscalls.c
index 9deb9edf68..370fa9e6fe 100644
--- a/cpu/arm_common/syscalls.c
+++ b/cpu/arm_common/syscalls.c
@@ -73,7 +73,7 @@ extern uintptr_t __heap3_max;       ///< maximum for end of heap memory space
 /*-----------------------------------------------------------------------------------*/
 void __assert_func(const char *file, int line, const char *func, const char *failedexpr)
 {
-    printf("#!assertion %s failed\n\t%s() in %s:%u\n", failedexpr, func, file, line);
+    printf("#!assertion %s failed\n\t%s() in %s:%d\n", failedexpr, func, file, line);
     _exit(3);
 }
 /*-----------------------------------------------------------------------------------*/
diff --git a/cpu/lpc1768/syscalls.c b/cpu/lpc1768/syscalls.c
index 1160a7c830..411ec00c8c 100644
--- a/cpu/lpc1768/syscalls.c
+++ b/cpu/lpc1768/syscalls.c
@@ -64,7 +64,7 @@ void heap_stats(void) {
 /*-----------------------------------------------------------------------------------*/
 void __assert_func(const char *file, int line, const char *func, const char *failedexpr)
 {
-	printf("#! assertion %s failed\n\t%s() in %s:%u\n", failedexpr, func, file, line );
+	printf("#! assertion %s failed\n\t%s() in %s:%d\n", failedexpr, func, file, line );
 	_exit(3);
 }
 /*-----------------------------------------------------------------------------------*/
diff --git a/sys/net/network_layer/sixlowpan/icmp.c b/sys/net/network_layer/sixlowpan/icmp.c
index 1ca7ff4d93..06a07a1ff6 100644
--- a/sys/net/network_layer/sixlowpan/icmp.c
+++ b/sys/net/network_layer/sixlowpan/icmp.c
@@ -270,7 +270,7 @@ void icmpv6_send_echo_request(ipv6_addr_t *destaddr, uint16_t id, uint16_t seq,
 
 #ifdef DEBUG_ENABLED
     char addr_str[IPV6_MAX_ADDR_STR_LEN];
-    printf("INFO: send echo request (id = %04x, seq = %d, data_len = %d) to: %s\n",
+    printf("INFO: send echo request (id = %04x, seq = %d, data_len = %zu) to: %s\n",
            id, seq, data_len, ipv6_addr_to_str(addr_str, IPV6_MAX_ADDR_STR_LEN,
                    &ipv6_buf->destaddr));
 #endif
@@ -309,7 +309,7 @@ void icmpv6_send_echo_reply(ipv6_addr_t *destaddr, uint16_t id, uint16_t seq, ui
 
 #ifdef DEBUG_ENABLED
     char addr_str[IPV6_MAX_ADDR_STR_LEN];
-    printf("INFO: send echo reply (id = %04x, seq = %d, data_len = %d) to: %s\n",
+    printf("INFO: send echo reply (id = %04x, seq = %d, data_len = %zu) to: %s\n",
            id, seq, data_len, ipv6_addr_to_str(addr_str, IPV6_MAX_ADDR_STR_LEN,
                    &ipv6_buf->destaddr));
 #endif
@@ -386,7 +386,7 @@ void recv_echo_req(void)
            ipv6_addr_to_str(addr_str, IPV6_MAX_ADDR_STR_LEN,
                             &ipv6_buf->srcaddr));
     printf("\n");
-    printf("id = 0x%04x, seq = %d, data_len = %d\n", NTOHS(echo_buf->id),
+    printf("id = 0x%04x, seq = %d, data_len = %zu\n", NTOHS(echo_buf->id),
            NTOHS(echo_buf->seq), data_len);
 
     for (size_t i = 0; i < data_len; i++) {
@@ -415,7 +415,7 @@ void recv_echo_repl(void)
            ipv6_addr_to_str(addr_str, IPV6_MAX_ADDR_STR_LEN,
                             &ipv6_buf->srcaddr));
     printf("\n");
-    printf("id = 0x%04x, seq = %d, data_len = %d\n", NTOHS(echo_buf->id),
+    printf("id = 0x%04x, seq = %d, data_len = %zu\n", NTOHS(echo_buf->id),
            NTOHS(echo_buf->seq), data_len);
 
     for (size_t i = 0; i < data_len; i++) {
diff --git a/sys/ps/ps.c b/sys/ps/ps.c
index dc6a29c688..30270b4161 100644
--- a/sys/ps/ps.c
+++ b/sys/ps/ps.c
@@ -67,7 +67,7 @@ void thread_print_all(void)
             stacksz -= thread_measure_stack_free(p->stack_start);
             printf("\t%3u | %-21s| %-8s %.1s | %3i | %5i (%5i) %p"
 #if SCHEDSTATISTICS
-                   " | %6.3f%% |  %8u"
+                   " | %6.3f%% |  %8d"
 #endif
                    "\n",
                    p->pid, p->name, sname, queued, p->priority, p->stack_size, stacksz, p->stack_start
diff --git a/sys/shell/commands/sc_id.c b/sys/shell/commands/sc_id.c
index 36389f192d..04653ab185 100644
--- a/sys/shell/commands/sc_id.c
+++ b/sys/shell/commands/sc_id.c
@@ -27,7 +27,7 @@ void _id_handler(int argc, char **argv)
     }
     else {
         long newid = atoi(argv[1]);
-        printf("Setting new id %lu\n", newid);
+        printf("Setting new id %ld\n", newid);
         sysconfig.id = newid;
 
         if (!config_save()) {
diff --git a/sys/shell/commands/sc_rpl.c b/sys/shell/commands/sc_rpl.c
index 2117a4d818..0fe6f327ab 100644
--- a/sys/shell/commands/sc_rpl.c
+++ b/sys/shell/commands/sc_rpl.c
@@ -47,7 +47,7 @@ void _rpl_route_handler(int argc, char **argv)
         }
     }
     puts("--------------------------------------------------------------------");
-    printf(" %d routing table entries\n", c);
+    printf(" %u routing table entries\n", c);
 
     puts("$");
 }
diff --git a/tests/test_posix_sleep/main.c b/tests/test_posix_sleep/main.c
index eb9fd4cca2..a8ea9b0299 100644
--- a/tests/test_posix_sleep/main.c
+++ b/tests/test_posix_sleep/main.c
@@ -34,7 +34,7 @@ int main(void)
     puts("sleep 1");
     for (int i = 0; i < 10; i++) {
         unsigned int s = i;
-        printf("calling sleep(%d)\n", s);
+        printf("calling sleep(%u)\n", s);
         sleep(s);
         puts("wake up");
     }
diff --git a/tests/test_queue_fairness/main.c b/tests/test_queue_fairness/main.c
index 3f1a10fa64..d8c9f63281 100644
--- a/tests/test_queue_fairness/main.c
+++ b/tests/test_queue_fairness/main.c
@@ -71,7 +71,7 @@ int main(void)
         int cur_iteration = (int) m.type;
         char *child = (char *) m.content.ptr;
 
-        printf("Received message from %s, iteration %u / %u: %s\n",
+        printf("Received message from %s, iteration %d / %u: %s\n",
                child, cur_iteration, NUM_ITERATIONS,
                cur_iteration >= last_iteration ? "okay" : "ERROR");