diff --git a/core/mutex.c b/core/mutex.c
index 53dd916a93..6fd891d49f 100644
--- a/core/mutex.c
+++ b/core/mutex.c
@@ -24,6 +24,7 @@
 #include <inttypes.h>
 #include <stdio.h>
 
+#include "cpu.h"
 #include "mutex.h"
 #include "thread.h"
 #include "sched.h"
diff --git a/cpu/sam0_common/periph/adc.c b/cpu/sam0_common/periph/adc.c
index 71764dba72..61a54e4945 100644
--- a/cpu/sam0_common/periph/adc.c
+++ b/cpu/sam0_common/periph/adc.c
@@ -389,14 +389,10 @@ void adc_continuous_begin(adc_res_t res)
 
 int32_t adc_continuous_sample(adc_t line)
 {
-    int val;
     assert(line < ADC_NUMOF);
+    assert(mutex_trylock(&_lock) == 0);
 
-    mutex_lock(&_lock);
-    val = _sample(line) << _shift;
-    mutex_unlock(&_lock);
-
-    return val;
+    return _sample(line) << _shift;
 }
 
 void adc_continuous_stop(void)