diff --git a/cpu/cortexm_common/cortexm_init.c b/cpu/cortexm_common/cortexm_init.c
index 1875da98fdbd79606defb73c96227d7f9607d6b7..dccee08e790f03dfcc480387b44126caa6fdaf3b 100644
--- a/cpu/cortexm_common/cortexm_init.c
+++ b/cpu/cortexm_common/cortexm_init.c
@@ -46,7 +46,7 @@ void cortexm_init(void)
     /* set SVC interrupt to same priority as the rest */
     NVIC_SetPriority(SVCall_IRQn, CPU_DEFAULT_IRQ_PRIO);
     /* initialize all vendor specific interrupts with the same value */
-    for (int i = 0; i < CPU_IRQ_NUMOF; i++) {
+    for (int i = 0; i < (int)CPU_IRQ_NUMOF; i++) {
         NVIC_SetPriority((IRQn_Type) i, CPU_DEFAULT_IRQ_PRIO);
     }
 
diff --git a/cpu/cortexm_common/mpu.c b/cpu/cortexm_common/mpu.c
index 27f103177cdafcb3ee4378d3050a12e729421bba..d29effdc412cad43e64422c11118d68f7c93db65 100644
--- a/cpu/cortexm_common/mpu.c
+++ b/cpu/cortexm_common/mpu.c
@@ -67,6 +67,9 @@ int mpu_configure(uint_fast8_t region, uintptr_t base, uint_fast32_t attr) {
 
     return 0;
 #else
+    (void)region;
+    (void)base;
+    (void)attr;
     return -1;
 #endif
 }
diff --git a/cpu/kinetis_common/periph/gpio.c b/cpu/kinetis_common/periph/gpio.c
index ffb14995b35d34782810450bab6adfb98239bfdf..001ac40ddc8df7f3a01ed3d2ceb36384c65fb6fe 100644
--- a/cpu/kinetis_common/periph/gpio.c
+++ b/cpu/kinetis_common/periph/gpio.c
@@ -145,7 +145,7 @@ static inline int get_ctx(int port, int pin)
  */
 static int get_free_ctx(void)
 {
-    for (int i = 0; i < CTX_NUMOF; i++) {
+    for (unsigned int i = 0; i < CTX_NUMOF; i++) {
         if (isr_ctx[i].cb == NULL) {
             return i;
         }
diff --git a/drivers/at86rf2xx/at86rf2xx.c b/drivers/at86rf2xx/at86rf2xx.c
index fbd06d80d941c5e823f9df010cd77d89a403324b..a34e802aeeebf9bcbb44947767df84619686e17b 100644
--- a/drivers/at86rf2xx/at86rf2xx.c
+++ b/drivers/at86rf2xx/at86rf2xx.c
@@ -77,7 +77,7 @@ void at86rf2xx_reset(at86rf2xx_t *dev)
     cpuid_get(cpuid);
 
 #if CPUID_LEN > IEEE802154_LONG_ADDRESS_LEN
-    for (int i = IEEE802154_LONG_ADDRESS_LEN; i < CPUID_LEN; i++) {
+    for (unsigned int i = IEEE802154_LONG_ADDRESS_LEN; i < CPUID_LEN; i++) {
         cpuid[i & 0x07] ^= cpuid[i];
     }
 #endif
diff --git a/drivers/at86rf2xx/at86rf2xx_netdev.c b/drivers/at86rf2xx/at86rf2xx_netdev.c
index 7e73624a6f2bb5cb19f1bb2841fee9d2de57d2ed..180d45460617c9208b585e8ebf213775fc68d36d 100644
--- a/drivers/at86rf2xx/at86rf2xx_netdev.c
+++ b/drivers/at86rf2xx/at86rf2xx_netdev.c
@@ -434,8 +434,8 @@ static int _set(netdev2_t *netdev, netopt_t opt, void *val, size_t len)
             }
             else {
                 uint8_t chan = ((uint8_t *)val)[0];
-                if (chan < AT86RF2XX_MIN_CHANNEL ||
-                    chan > AT86RF2XX_MAX_CHANNEL) {
+                if ((chan < AT86RF2XX_MIN_CHANNEL) ||
+                    (chan > AT86RF2XX_MAX_CHANNEL)) {
                     res = -EINVAL;
                     break;
                 }
diff --git a/sys/auto_init/saul/auto_init_adc.c b/sys/auto_init/saul/auto_init_adc.c
index 16b020d4344d408107eabc99df93d70f6ade2ad3..af94cff45a946a7c00069aae227c832b6fc73e99 100644
--- a/sys/auto_init/saul/auto_init_adc.c
+++ b/sys/auto_init/saul/auto_init_adc.c
@@ -55,7 +55,7 @@ extern saul_driver_t adc_saul_driver;
 void auto_init_adc(void)
 {
     DEBUG("auto init SAUL ADC\n");
-    for (int i = 0; i < SAUL_ADC_NUMOF; i++) {
+    for (unsigned int i = 0; i < SAUL_ADC_NUMOF; i++) {
         const saul_adc_params_t *p = &saul_adc_params[i];
         saul_adcs[i] = p;
 
diff --git a/sys/auto_init/saul/auto_init_gpio.c b/sys/auto_init/saul/auto_init_gpio.c
index 454c1d0b82ebaf7026634ddc917d4ea8b67dfa17..5795a21cc3e6dd07e7a5bd9d99f611138869978b 100644
--- a/sys/auto_init/saul/auto_init_gpio.c
+++ b/sys/auto_init/saul/auto_init_gpio.c
@@ -53,7 +53,7 @@ extern saul_driver_t gpio_saul_driver;
 void auto_init_gpio(void)
 {
     DEBUG("auto init gpio SAUL\n");
-    for (int i = 0; i < SAUL_GPIO_NUMOF; i++) {
+    for (unsigned int i = 0; i < SAUL_GPIO_NUMOF; i++) {
         const saul_gpio_params_t *p = &saul_gpio_params[i];
 
         DEBUG("[auto_init_saul] initializing direct GPIO\n");
diff --git a/sys/auto_init/saul/auto_init_isl29020.c b/sys/auto_init/saul/auto_init_isl29020.c
index c6e0497296755deb89ac60d5f239f8b9af3b7460..24323bb1fc7fa3f4b92c31e13da56b587829efdf 100644
--- a/sys/auto_init/saul/auto_init_isl29020.c
+++ b/sys/auto_init/saul/auto_init_isl29020.c
@@ -51,7 +51,7 @@ extern saul_driver_t isl29020_saul_driver;
 
 void auto_init_isl29020(void)
 {
-    for (int i = 0; i < ISL29020_NUM; i++) {
+    for (unsigned int i = 0; i < ISL29020_NUM; i++) {
         const isl29020_params_t *p = &isl29020_params[i];
 
         DEBUG("[auto_init_saul] initializing isl29020 light sensor\n");
diff --git a/sys/auto_init/saul/auto_init_l3g4200d.c b/sys/auto_init/saul/auto_init_l3g4200d.c
index a4a9a109ed55ac381a1f2d0659e9561de26f598c..f0fe7591023a31986474b6333bac6e01407faf72 100644
--- a/sys/auto_init/saul/auto_init_l3g4200d.c
+++ b/sys/auto_init/saul/auto_init_l3g4200d.c
@@ -51,7 +51,7 @@ extern saul_driver_t l3g4200d_saul_driver;
 
 void auto_init_l3g4200d(void)
 {
-    for (int i = 0; i < L3G4200D_NUM; i++) {
+    for (unsigned int i = 0; i < L3G4200D_NUM; i++) {
         const l3g4200d_params_t *p = &l3g4200d_params[i];
 
         DEBUG("[auto_init_saul] initializing l3g4200d gyroscope\n");
diff --git a/sys/auto_init/saul/auto_init_lis3dh.c b/sys/auto_init/saul/auto_init_lis3dh.c
index 12f5a018c1566300be80340fa52424563d8db546..59ca663d797ca091417241bfed0c536346391bb0 100644
--- a/sys/auto_init/saul/auto_init_lis3dh.c
+++ b/sys/auto_init/saul/auto_init_lis3dh.c
@@ -51,7 +51,7 @@ extern saul_driver_t lis3dh_saul_driver;
 
 void auto_init_lis3dh(void)
 {
-    for (int i = 0; i < LIS3DH_NUM; i++) {
+    for (unsigned int i = 0; i < LIS3DH_NUM; i++) {
         const lis3dh_params_t *p = &lis3dh_params[i];
         int res;
 
diff --git a/sys/auto_init/saul/auto_init_lps331ap.c b/sys/auto_init/saul/auto_init_lps331ap.c
index e505a9e32b3e9b741c14cede6444bacf4ee3234e..80fec304420e8f64db98809ca52ed72392351d30 100644
--- a/sys/auto_init/saul/auto_init_lps331ap.c
+++ b/sys/auto_init/saul/auto_init_lps331ap.c
@@ -51,7 +51,7 @@ extern saul_driver_t lps331ap_saul_driver;
 
 void auto_init_lps331ap(void)
 {
-    for (int i = 0; i < LPS331AP_NUM; i++) {
+    for (unsigned int i = 0; i < LPS331AP_NUM; i++) {
         const lps331ap_params_t *p = &lps331ap_params[i];
 
         DEBUG("[auto_init_saul] initializing lps331ap pressure sensor\n");
diff --git a/sys/auto_init/saul/auto_init_lsm303dlhc.c b/sys/auto_init/saul/auto_init_lsm303dlhc.c
index 3c4e71ab93b010aa3bfa36c43a5c6725d473f66b..fdf9b9df2a3a16569e7a4941fabed9013a1886a2 100644
--- a/sys/auto_init/saul/auto_init_lsm303dlhc.c
+++ b/sys/auto_init/saul/auto_init_lsm303dlhc.c
@@ -53,7 +53,7 @@ extern saul_driver_t lsm303dlhc_saul_mag_driver;
 
 void auto_init_lsm303dlhc(void)
 {
-    for (int i = 0; i < LSM303DLHC_NUM; i++) {
+    for (unsigned int i = 0; i < LSM303DLHC_NUM; i++) {
         const lsm303dlhc_params_t *p = &lsm303dlhc_params[i];
 
         DEBUG("[auto_init_saul] initializing lsm303dlhc acc/mag sensor\n");
diff --git a/sys/auto_init/saul/auto_init_mma8652.c b/sys/auto_init/saul/auto_init_mma8652.c
index bb97c115be262495e8e6d11f3f7e4cea969f6f1d..5d6d2d0a81e914399b19c91f3913d5d2f398c01d 100644
--- a/sys/auto_init/saul/auto_init_mma8652.c
+++ b/sys/auto_init/saul/auto_init_mma8652.c
@@ -52,7 +52,7 @@ extern saul_driver_t mma8652_saul_driver;
 
 void auto_init_mma8652(void)
 {
-    for (int i = 0; i < MMA8652_NUM; i++) {
+    for (unsigned int i = 0; i < MMA8652_NUM; i++) {
         const mma8652_params_t *p = &mma8652_params[i];
 
         DEBUG("[auto_init_saul] initializing mma8652 acc sensor\n");