diff --git a/cpu/stm32l1/periph/adc.c b/cpu/stm32l1/periph/adc.c
index 497f020012..8cebee2fc9 100644
--- a/cpu/stm32l1/periph/adc.c
+++ b/cpu/stm32l1/periph/adc.c
@@ -152,7 +152,7 @@ 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)
 {
     int sample;