diff --git a/cpu/sam0_common/include/periph_cpu_common.h b/cpu/sam0_common/include/periph_cpu_common.h
index a2506d4a40..212063765c 100644
--- a/cpu/sam0_common/include/periph_cpu_common.h
+++ b/cpu/sam0_common/include/periph_cpu_common.h
@@ -128,7 +128,7 @@ typedef struct {
     uart_rxpad_t rx_pad;    /**< pad selection for RX line */
     uart_txpad_t tx_pad;    /**< pad selection for TX line */
     uint8_t runstdby;       /**< allow SERCOM to run in standby mode */
-    uint8_t gclk_src;       /**< GCLK source which supplys SERCOM */
+    uint32_t gclk_src;      /**< GCLK source which supplys SERCOM */
 } uart_conf_t;
 
 /**