diff --git a/TODO b/TODO
index d9277255..de240dda 100644
--- a/TODO
+++ b/TODO
@@ -185,6 +185,8 @@ Line -1 and -3 should mention CATEGORIE, not CATEGORY.
 
 * Bison 3.8
 ** Rewrite glr.cc (currently glr2.cc)
+*** custom error messages
+
 *** Remove jumps
 We can probably replace setjmp/longjmp with exceptions.  That would help
 tremendously other languages such as D and Java that probably have no
diff --git a/data/skeletons/glr.c b/data/skeletons/glr.c
index 117c996b..fab3733f 100644
--- a/data/skeletons/glr.c
+++ b/data/skeletons/glr.c
@@ -2174,10 +2174,10 @@ yypcontext_token (const yyGLRStack *yystackp)
 }
 
 ]b4_locations_if([[/* The location of the lookahead of this context.  */
-static YYLTYPE *
+static const YYLTYPE *
 yypcontext_location (const yyGLRStack *yystackp) YY_ATTRIBUTE_UNUSED;
 
-static YYLTYPE *
+static const YYLTYPE *
 yypcontext_location (const yyGLRStack *yystackp)
 {
   YY_USE (yystackp);
diff --git a/tests/calc.at b/tests/calc.at
index cd4b50a1..47ef720c 100644
--- a/tests/calc.at
+++ b/tests/calc.at
@@ -1469,6 +1469,8 @@ AT_CHECK_CALC_GLR_CC([%debug])
 AT_CHECK_CALC_GLR_CC([%define parse.error verbose %debug %name-prefix "calc" %verbose])
 AT_CHECK_CALC_GLR_CC([%define parse.error verbose %debug %name-prefix "calc" %define api.token.prefix {TOK_} %verbose])
 
+AT_CHECK_CALC_GLR_CC([%define parse.error custom %locations %header %name-prefix "calc" %verbose])
+
 AT_CHECK_CALC_GLR_CC([%locations %header %define parse.error verbose %debug %name-prefix "calc" %verbose %parse-param {semantic_value *result}{int *count}{int *nerrs}])
 AT_CHECK_CALC_GLR_CC([%locations %header %define parse.error verbose %debug %define api.prefix {calc} %verbose %parse-param {semantic_value *result}{int *count}{int *nerrs}])