diff --git a/cpu/kinetis/periph/adc.c b/cpu/kinetis/periph/adc.c
index 2648637578..3b9b78cbd0 100644
--- a/cpu/kinetis/periph/adc.c
+++ b/cpu/kinetis/periph/adc.c
@@ -207,7 +207,7 @@ int adc_init(adc_t line)
     return res;
 }
 
-int adc_sample(adc_t line, adc_res_t res)
+int32_t adc_sample(adc_t line, adc_res_t res)
 {
     int sample;