diff --git a/stlinkv3_spi.c b/stlinkv3_spi.c
index d2988b6..d56f305 100644
--- a/stlinkv3_spi.c
+++ b/stlinkv3_spi.c
@@ -323,7 +323,7 @@
 	return 0;
 }
 
-static int stlinkv3_spi_transmit(struct flashctx *flash,
+static int stlinkv3_spi_transmit(const struct flashctx *flash,
 				 unsigned int write_cnt,
 				 unsigned int read_cnt,
 				 const unsigned char *write_arr,