diff --git a/cpu/cortex-m3_common/atomic_arch.c b/cpu/cortex-m3_common/atomic_arch.c
index 9b51df0e58..1ee7f4fc50 100644
--- a/cpu/cortex-m3_common/atomic_arch.c
+++ b/cpu/cortex-m3_common/atomic_arch.c
@@ -10,23 +10,37 @@
  * @ingroup     cpu_cortexm3_common
  * @{
  *
- * @file        atomic_arch.c
+ * @file
  * @brief       Implementation of the kernels atomic interface
  *
  * @author      Stefan Pfeiffer <stefan.pfeiffer@fu-berlin.de>
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ * @author      Joakim Gebart <joakim.gebart@eistec.se>
  *
  * @}
  */
 
-#include "arch/atomic_arch.h"
+#include <stdint.h>
+#include "atomic.h"
 #include "irq.h"
+#include "cpu.h"
 
-unsigned int atomic_arch_set_return(unsigned int *to_set, unsigned int value)
+int atomic_cas(atomic_int_t *var, int old, int now)
 {
-    disableIRQ();
-    unsigned int old = *to_set;
-    *to_set = value;
-    enableIRQ();
-    return old;
+    int tmp;
+    int status;
+
+    /* Load exclusive */
+    tmp = __LDREXW((volatile uint32_t *)(&ATOMIC_VALUE(*var)));
+
+    if (tmp != old) {
+        /* Clear memory exclusivity */
+        __CLREX();
+        return 0;
+    }
+
+    /* Try to write the new value */
+    status = __STREXW(now, (volatile uint32_t *)(&ATOMIC_VALUE(*var)));
+
+    return (status == 0);
 }
diff --git a/cpu/cortex-m3_common/include/cpu.h b/cpu/cortex-m3_common/include/cpu.h
index 6ace208af4..b72a1d768c 100644
--- a/cpu/cortex-m3_common/include/cpu.h
+++ b/cpu/cortex-m3_common/include/cpu.h
@@ -23,13 +23,13 @@
  * @author      Joakim Gebart <joakim.gebart@eistec.se>
  */
 
-#ifndef __CORTEXM_COMMON_H
-#define __CORTEXM_COMMON_H
+#ifndef CORTEXM_COMMON_H_
+#define CORTEXM_COMMON_H_
 
 /**
  * @brief Cortex-M3 has architecture specific atomic operations in atomic_arch.c.
  */
-#define ARCH_HAS_ATOMIC_INT 1
+#define ARCH_HAS_ATOMIC_COMPARE_AND_SWAP 1
 
 #include "cpu-conf.h"
 
@@ -55,5 +55,5 @@ void cpu_init(void);
 }
 #endif
 
-#endif /* __CORTEXM_COMMON_H */
+#endif /* CORTEXM_COMMON_H_ */
 /** @} */