diff --git a/drivers/flash/flash_stm32.h b/drivers/flash/flash_stm32.h
index dd8628f81d7..e0fba89a550 100644
--- a/drivers/flash/flash_stm32.h
+++ b/drivers/flash/flash_stm32.h
@@ -257,6 +257,12 @@ static inline bool flash_stm32_range_exists(const struct device *dev,
 }
 #endif	/* CONFIG_FLASH_PAGE_LAYOUT */
 
+static inline bool flash_stm32_valid_write(off_t offset, uint32_t len)
+{
+	return ((offset % FLASH_STM32_WRITE_BLOCK_SIZE == 0) &&
+		(len % FLASH_STM32_WRITE_BLOCK_SIZE == 0U));
+}
+
 bool flash_stm32_valid_range(const struct device *dev, off_t offset,
 			     uint32_t len, bool write);
 
diff --git a/drivers/flash/flash_stm32l5x.c b/drivers/flash/flash_stm32l5x.c
index a0b692b45c8..b4381289ad1 100644
--- a/drivers/flash/flash_stm32l5x.c
+++ b/drivers/flash/flash_stm32l5x.c
@@ -128,7 +128,7 @@ static int icache_wait_for_invalidate_complete(void)
 #endif /* CONFIG_SOC_SERIES_STM32H5X */
 
 /*
- * offset and len must be aligned on 8 for write,
+ * offset and len must be aligned on write-block-size for write,
  * positive and not beyond end of flash
  */
 bool flash_stm32_valid_range(const struct device *dev, off_t offset,
@@ -149,8 +149,10 @@ bool flash_stm32_valid_range(const struct device *dev, off_t offset,
 		}
 	}
 
-	return (!write || (offset % 8 == 0 && len % 8 == 0U)) &&
-		flash_stm32_range_exists(dev, offset, len);
+	if (write && !flash_stm32_valid_write(offset, len)) {
+		return false;
+	}
+	return flash_stm32_range_exists(dev, offset, len);
 }
 
 static int write_dword(const struct device *dev, off_t offset, uint64_t val)