diff --git a/include/haproxy/http_htx.h b/include/haproxy/http_htx.h
index fbd4438..d807584 100644
--- a/include/haproxy/http_htx.h
+++ b/include/haproxy/http_htx.h
@@ -33,7 +33,7 @@
 extern struct http_reply http_err_replies[HTTP_ERR_SIZE];
 extern struct list http_errors_list;
 
-struct htx_sl *http_get_stline(struct htx *htx);
+struct htx_sl *http_get_stline(const struct htx *htx);
 size_t http_get_hdrs_size(struct htx *htx);
 int http_find_header(const struct htx *htx, const struct ist name, struct http_hdr_ctx *ctx, int full);
 int http_find_str_header(const struct htx *htx, const struct ist name, struct http_hdr_ctx *ctx, int full);
diff --git a/src/http_htx.c b/src/http_htx.c
index fcfadce..a7951c0 100644
--- a/src/http_htx.c
+++ b/src/http_htx.c
@@ -60,7 +60,7 @@
  * if the start-line is undefined (first == -1). Otherwise, it returns the
  * pointer on the htx_sl structure.
  */
-struct htx_sl *http_get_stline(struct htx *htx)
+struct htx_sl *http_get_stline(const struct htx *htx)
 {
 	struct htx_blk *blk;