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");