diff --git a/lib/asn1/parse.y b/lib/asn1/parse.y
index b70da99e0..2622a7eb0 100644
--- a/lib/asn1/parse.y
+++ b/lib/asn1/parse.y
@@ -49,7 +49,7 @@ RCSID("$Id$");
 
 static Type *new_type (Typetype t);
 static Type *new_tag(int tagclass, int tagvalue, int tagenv, Type *oldtype);
-void yyerror (char *);
+void yyerror (const char *);
 static struct objid *new_objid(const char *label, int value);
 static void add_oid_to_tail(struct objid *, struct objid *);
 static void fix_labels(Symbol *s);
@@ -810,7 +810,7 @@ ObjectIdentifierValue: objid
 %%
 
 void
-yyerror (char *s)
+yyerror (const char *s)
 {
      error_message ("%s\n", s);
 }