diff --git a/sst28sf040.c b/sst28sf040.c
index 52e4256..4d8cb66 100644
--- a/sst28sf040.c
+++ b/sst28sf040.c
@@ -77,8 +77,7 @@
 }
 
 /* chunksize is 1 */
-int write_28sf040(struct flashctx *flash, uint8_t *src, unsigned int start,
-		  unsigned int len)
+int write_28sf040(struct flashctx *flash, const uint8_t *src, unsigned int start, unsigned int len)
 {
 	int i;
 	chipaddr bios = flash->virtual_memory;