diff --git a/cpu/sam0_common/include/cpu_conf.h b/cpu/sam0_common/include/cpu_conf.h
index e954eb139a..48c1658bcb 100644
--- a/cpu/sam0_common/include/cpu_conf.h
+++ b/cpu/sam0_common/include/cpu_conf.h
@@ -42,9 +42,15 @@ extern "C" {
  * @{
  */
 /* a flashpage in RIOT is mapped to a flash row on the SAM0s */
-#define FLASHPAGE_SIZE      (256U)
+#define FLASHPAGE_SIZE             (256U)
 /* one SAM0 row contains 4 SAM0 pages -> 4x the amount of RIOT flashpages */
-#define FLASHPAGE_NUMOF     (FLASH_NB_OF_PAGES / 4)
+#define FLASHPAGE_NUMOF            (FLASH_NB_OF_PAGES / 4)
+/* The minimum block size which can be written is 16B. However, the erase
+ * block is always FLASHPAGE_SIZE (SAM0 row).
+ */
+#define FLASHPAGE_RAW_BLOCKSIZE    (16)
+/* Writing should be always 4 byte aligned */
+#define FLASHPAGE_RAW_ALIGNMENT    (4)
 /** @} */
 
 #ifdef __cplusplus
diff --git a/cpu/sam0_common/periph/flashpage.c b/cpu/sam0_common/periph/flashpage.c
index a9e72c69a0..ee499d6ba8 100644
--- a/cpu/sam0_common/periph/flashpage.c
+++ b/cpu/sam0_common/periph/flashpage.c
@@ -58,19 +58,18 @@ static void _lock(void)
 
 void flashpage_write_raw(void *target_addr, void *data, size_t len)
 {
-    /* sam[dlr]21 can only write whole flash pages.
-     * Mind the use of the ATMEL FLASH_PAGE_SIZE (64B) define vs.
-     * FLASHPAGE_SIZE (256B) as defined by RIOT.
-     * The actual minimal block size for writing is 16B, thus we
-     * assert we don't write less than that.
+    /* The actual minimal block size for writing is 16B, thus we
+     * assert we write on multiples and no less of that length.
      */
-    assert(!(len % (FLASH_PAGE_SIZE / 4)));
+    assert(!(len % FLASHPAGE_RAW_BLOCKSIZE));
 
     /* ensure 4 byte aligned writes */
-    assert(!(((unsigned)target_addr & 0x3) || ((unsigned)data & 0x3)));
+    assert(!(((unsigned)target_addr % FLASHPAGE_RAW_ALIGNMENT) ||
+            ((unsigned)data % FLASHPAGE_RAW_ALIGNMENT)));
 
     /* ensure the length doesn't exceed the actual flash size */
-    assert((target_addr + len) < (CPU_FLASH_BASE + (FLASHPAGE_SIZE * FLASHPAGE_NUMOF)));
+    assert(((uint8_t*)target_addr + len) <
+           (CPU_FLASH_BASE + (FLASHPAGE_SIZE * FLASHPAGE_NUMOF)));
 
     uint32_t *dst = (uint32_t *)target_addr;
     uint32_t *data_addr = (uint32_t *)data;