diff --git a/cpu/sam0_common/periph/adc.c b/cpu/sam0_common/periph/adc.c
index 7760a2b935..c1d11bf2a2 100644
--- a/cpu/sam0_common/periph/adc.c
+++ b/cpu/sam0_common/periph/adc.c
@@ -164,7 +164,7 @@ int adc_init(adc_t line)
     return 0;
 }
 
-int adc_sample(adc_t line, adc_res_t res)
+int32_t adc_sample(adc_t line, adc_res_t res)
 {
     if (line >= ADC_NUMOF) {
         DEBUG("adc: line arg not applicable\n");