diff --git a/sys/arm/include/atomic.h b/sys/arm/include/atomic.h
index 9785ba68a8bc..ec1fd9f1ee0b 100644
--- a/sys/arm/include/atomic.h
+++ b/sys/arm/include/atomic.h
@@ -75,7 +75,7 @@ static __inline uint32_t
 __swp(uint32_t val, volatile uint32_t *ptr)
 {
 	__asm __volatile("swp	%0, %1, [%2]"
-	    : "=r" (val) : "r" (val) , "r" (ptr) : "memory");
+	    : "=&r" (val) : "r" (val) , "r" (ptr) : "memory");
 	return (val);
 }