diff --git a/usbblaster_spi.c b/usbblaster_spi.c
index e2a0a4f..46de86c 100644
--- a/usbblaster_spi.c
+++ b/usbblaster_spi.c
@@ -179,7 +179,7 @@
 }
 
 /* Returns 0 upon success, a negative number upon errors. */
-static int usbblaster_spi_send_command(struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
+static int usbblaster_spi_send_command(const struct flashctx *flash, unsigned int writecnt, unsigned int readcnt,
 				       const unsigned char *writearr, unsigned char *readarr)
 {
 	uint8_t cmd;