diff --git a/drivers/st/io/io_stm32image.c b/drivers/st/io/io_stm32image.c
index 48bb4d3..70e4be3 100644
--- a/drivers/st/io/io_stm32image.c
+++ b/drivers/st/io/io_stm32image.c
@@ -250,6 +250,7 @@
 	uint8_t *local_buffer;
 	boot_api_image_header_t *header =
 		(boot_api_image_header_t *)first_lba_buffer;
+	size_t hdr_sz = sizeof(boot_api_image_header_t);
 
 	assert(entity != NULL);
 	assert(buffer != 0U);
@@ -286,16 +287,13 @@
 		}
 
 		/* Part of image already loaded with the header */
-		memcpy(local_buffer, (uint8_t *)first_lba_buffer +
-		       sizeof(boot_api_image_header_t),
-		       MAX_LBA_SIZE - sizeof(boot_api_image_header_t));
-		local_buffer += MAX_LBA_SIZE - sizeof(boot_api_image_header_t);
+		memcpy(local_buffer, (uint8_t *)first_lba_buffer + hdr_sz,
+		       MAX_LBA_SIZE - hdr_sz);
+		local_buffer += MAX_LBA_SIZE - hdr_sz;
 		offset = MAX_LBA_SIZE;
 
 		/* New image length to be read */
-		local_length = round_up(length -
-					((MAX_LBA_SIZE) -
-					 sizeof(boot_api_image_header_t)),
+		local_length = round_up(length - ((MAX_LBA_SIZE) - hdr_sz),
 					stm32image_dev.lba_size);
 
 		if ((header->load_address != 0U) &&
@@ -326,7 +324,7 @@
 				 local_length, length_read);
 
 		/* Adding part of size already read from header */
-		*length_read += MAX_LBA_SIZE - sizeof(boot_api_image_header_t);
+		*length_read += MAX_LBA_SIZE - hdr_sz;
 
 		if (result != 0) {
 			ERROR("%s: io_read (%i)\n", __func__, result);