diff --git a/src/document/html/parser.c b/src/document/html/parser.c
index 093f74b77..79db9c4b5 100644
--- a/src/document/html/parser.c
+++ b/src/document/html/parser.c
@@ -177,7 +177,7 @@ put_chrs(struct html_context *html_context, const char *start, int len)
 
 void
 set_fragment_identifier(struct html_context *html_context,
-                        char *attr_name, char *attr)
+                        char *attr_name, const char *attr)
 {
 	char *id_attr;
 
diff --git a/src/document/html/parser.h b/src/document/html/parser.h
index a567604f0..e7f690eaa 100644
--- a/src/document/html/parser.h
+++ b/src/document/html/parser.h
@@ -190,7 +190,7 @@ void done_html_parser_state(struct html_context *html_context, void *state);
 
 int get_bgcolor(struct html_context *html_context, char *a, color_T *rgb);
 void set_fragment_identifier(struct html_context *html_context,
-                             char *attr_name, char *attr);
+                             char *attr_name, const char *attr);
 void add_fragment_identifier(struct html_context *html_context,
                              struct part *, char *attr);