diff --git a/lib/fwu_updates/fwu_mtd.c b/lib/fwu_updates/fwu_mtd.c
index b73111a..69cd3d7 100644
--- a/lib/fwu_updates/fwu_mtd.c
+++ b/lib/fwu_updates/fwu_mtd.c
@@ -175,8 +175,10 @@
 
 		l = strlen(buf);
 		/* Replace the last ';' with '&' if there is another image. */
-		if (i != CONFIG_FWU_NUM_IMAGES_PER_BANK - 1 && l)
-			buf[l - 1] = '&';
+		if (i != CONFIG_FWU_NUM_IMAGES_PER_BANK - 1 && l) {
+			buf[l] = '&';
+			buf++;
+		}
 		len -= l;
 		buf += l;
 	}