diff --git a/src/document/html/parser.c b/src/document/html/parser.c
index 06f98cec..093f74b7 100644
--- a/src/document/html/parser.c
+++ b/src/document/html/parser.c
@@ -53,7 +53,7 @@
 
 static int
 extract_color(struct html_context *html_context, char *a,
-	      char *attribute, color_T *rgb)
+	      const char *attribute, color_T *rgb)
 {
 	char *value;
 	int retval;
@@ -69,7 +69,7 @@ extract_color(struct html_context *html_context, char *a,
 
 int
 get_color(struct html_context *html_context, char *a,
-	  char *attribute, color_T *rgb)
+	  const char *attribute, color_T *rgb)
 {
 	if (!use_document_fg_colors(html_context->options))
 		return -1;
diff --git a/src/document/html/parser.h b/src/document/html/parser.h
index e079a683..a567604f 100644
--- a/src/document/html/parser.h
+++ b/src/document/html/parser.h
@@ -214,7 +214,7 @@ get_image_map(char *head, char *pos, char *eof,
  * will only add two line-breaks for the entire run of <br>'s. */
 void ln_break(struct html_context *html_context, int n);
 
-int get_color(struct html_context *html_context, char *a, char *c, color_T *rgb);
+int get_color(struct html_context *html_context, char *a, const char *c, color_T *rgb);
 
 int get_color2(struct html_context *html_context, char *value_value, color_T *rgb);