diff --git a/cpu/sam3/periph/adc.c b/cpu/sam3/periph/adc.c
index 1c2651e670..7cd58b652e 100644
--- a/cpu/sam3/periph/adc.c
+++ b/cpu/sam3/periph/adc.c
@@ -68,7 +68,7 @@ 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)
 {
     assert(line < ADC_NUMOF);