diff --git a/cpu/sam0_common/periph/i2c.c b/cpu/sam0_common/periph/i2c.c
index e7c62470b1..a0f4cefe53 100644
--- a/cpu/sam0_common/periph/i2c.c
+++ b/cpu/sam0_common/periph/i2c.c
@@ -22,6 +22,7 @@
  * @}
  */
 
+#include <assert.h>
 #include <stdint.h>
 #include <errno.h>
 
@@ -164,11 +165,10 @@ int i2c_acquire(i2c_t dev)
     return 0;
 }
 
-int i2c_release(i2c_t dev)
+void i2c_release(i2c_t dev)
 {
     assert(dev < I2C_NUMOF);
     mutex_unlock(&locks[dev]);
-    return 0;
 }
 
 int i2c_read_bytes(i2c_t dev, uint16_t addr,