diff --git a/cpu/mips_pic32_common/periph/gpio.c b/cpu/mips_pic32_common/periph/gpio.c
index 210b83179f..ab9435d644 100644
--- a/cpu/mips_pic32_common/periph/gpio.c
+++ b/cpu/mips_pic32_common/periph/gpio.c
@@ -106,7 +106,7 @@ static PIC32_GPIO_T base_address[] = {
 static inline int check_valid_port(uint8_t port)
 {
     return port < (sizeof(base_address)/sizeof(base_address[0]))
-        && base_address[port].gpio != 0;
+        && base_address[port].gpio != NULL;
 }
 
 int gpio_init(gpio_t pin, gpio_mode_t mode)
diff --git a/sys/posix/sockets/posix_sockets.c b/sys/posix/sockets/posix_sockets.c
index dfa7a9bf8f..af85174c84 100644
--- a/sys/posix/sockets/posix_sockets.c
+++ b/sys/posix/sockets/posix_sockets.c
@@ -265,7 +265,7 @@ static int socket_close(vfs_file_t *filp)
 #endif
 #ifdef MODULE_SOCK_TCP
             case SOCK_STREAM:
-                if (s->queue_array == 0) {
+                if (s->queue_array == NULL) {
                     sock_tcp_disconnect(&s->sock->tcp.sock);
                 }
                 else {
@@ -863,7 +863,7 @@ static ssize_t socket_recvfrom(socket_t *s, void *restrict buffer,
             res = -EOPNOTSUPP;
             break;
     }
-    if ((res >= 0) && (address != NULL) && (address_len != 0)) {
+    if ((res >= 0) && (address != NULL) && (address_len != NULL)) {
         switch (s->type) {
 #ifdef MODULE_SOCK_TCP
             case SOCK_STREAM:
diff --git a/sys/xtimer/xtimer_core.c b/sys/xtimer/xtimer_core.c
index c299fac2d5..1ac645838e 100644
--- a/sys/xtimer/xtimer_core.c
+++ b/sys/xtimer/xtimer_core.c
@@ -487,7 +487,8 @@ overflow:
      * next timer period and check again for expired
      * timers.*/
     if (reference > _xtimer_lltimer_now()) {
-        DEBUG("_timer_callback: overflowed while executing callbacks. %i\n", timer_list_head != 0);
+        DEBUG("_timer_callback: overflowed while executing callbacks. %i\n",
+              timer_list_head != NULL);
         _next_period();
         reference = 0;
         goto overflow;