diff --git a/cpu/stm32/include/cpu_conf.h b/cpu/stm32/include/cpu_conf.h
index fdc37fbb7f..35e10aaab7 100644
--- a/cpu/stm32/include/cpu_conf.h
+++ b/cpu/stm32/include/cpu_conf.h
@@ -116,6 +116,11 @@ extern "C" {
 #define FLASHPAGE_SIZE                  (128U)
 #endif
 
+#if defined(CPU_FAM_STM32L0) || defined(CPU_FAM_STM32L1) || \
+    defined(CPU_FAM_STM32L4)
+#define FLASHPAGE_ERASE_STATE           (0x00U)
+#endif
+
 #ifdef FLASHPAGE_SIZE
 #define FLASHPAGE_NUMOF                 (STM32_FLASHSIZE / FLASHPAGE_SIZE)
 #endif
diff --git a/drivers/include/periph/flashpage.h b/drivers/include/periph/flashpage.h
index 2153b84f95..9080e3336c 100644
--- a/drivers/include/periph/flashpage.h
+++ b/drivers/include/periph/flashpage.h
@@ -85,6 +85,15 @@ extern "C" {
 #define FLASHPAGE_WRITE_BLOCK_ALIGNMENT
 #endif
 
+/**
+ * @def FLASHPAGE_ERASE_STATE
+ *
+ * @brief   State of an erased byte in memory
+ */
+#if defined(DOXYGEN) || !defined(FLASHPAGE_ERASE_STATE)
+#define FLASHPAGE_ERASE_STATE           (0xFFU)
+#endif
+
 /**
  * @def     PERIPH_FLASHPAGE_CUSTOM_PAGESIZES
  *
diff --git a/sys/riotboot/flashwrite.c b/sys/riotboot/flashwrite.c
index e5ef3134ae..2088f67953 100644
--- a/sys/riotboot/flashwrite.c
+++ b/sys/riotboot/flashwrite.c
@@ -30,11 +30,6 @@
 #define LOG_PREFIX "riotboot_flashwrite: "
 #include "log.h"
 
-/**
- * @brief Magic number used to invalidate a slot
- */
-#define INVALIDATE_HDR                  0xAA
-
 static inline size_t min(size_t a, size_t b)
 {
     return a <= b ? a : b;
@@ -178,10 +173,14 @@ int riotboot_flashwrite_invalidate(int slot)
         return -2;
     }
 
-    uint8_t data_flash[4];
-    memset(data_flash, INVALIDATE_HDR, sizeof(data_flash));
+    /* invalidate header (checksum and magic number must be invalidated),
+       write the whole header to avoid running in memory alignment issues
+       with FLASHPAGE_WRITE_BLOCK_SIZE */
+    riotboot_hdr_t tmp_hdr;
+    memset(&tmp_hdr, (~FLASHPAGE_ERASE_STATE), sizeof(riotboot_hdr_t));
 
-    flashpage_write((void *)riotboot_slot_get_hdr(slot), data_flash, sizeof(data_flash));
+    flashpage_write((void *)riotboot_slot_get_hdr(slot), &tmp_hdr,
+                    sizeof(riotboot_hdr_t));
 
     return 0;
 }