diff --git a/lib/asn1/der.h b/lib/asn1/der.h
index f861449a6..dfa534d41 100644
--- a/lib/asn1/der.h
+++ b/lib/asn1/der.h
@@ -71,8 +71,8 @@ size_t length_general_string (general_string *data);
 size_t length_octet_string (octet_string *k);
 size_t length_generalized_time (time_t *t);
 
-void copy_general_string (general_string *from, general_string *to);
-void copy_octet_string (octet_string *from, octet_string *to);
+void copy_general_string (const general_string *from, general_string *to);
+void copy_octet_string (const octet_string *from, octet_string *to);
 
 int fix_dce(int reallen, int *len);
 
diff --git a/lib/asn1/der_copy.c b/lib/asn1/der_copy.c
index a4265a225..5dfe87002 100644
--- a/lib/asn1/der_copy.c
+++ b/lib/asn1/der_copy.c
@@ -3,14 +3,14 @@
 RCSID("$Id$");
 
 void
-copy_general_string (general_string *from, general_string *to)
+copy_general_string (const general_string *from, general_string *to)
 {
     *to = malloc(strlen(*from) + 1);
     strcpy(*to, *from);
 }
 
 void
-copy_octet_string (octet_string *from, octet_string *to)
+copy_octet_string (const octet_string *from, octet_string *to)
 {
     to->length = from->length;
     to->data = malloc(to->length);
diff --git a/lib/asn1/gen_copy.c b/lib/asn1/gen_copy.c
index 8ee9065cd..7ce72884b 100644
--- a/lib/asn1/gen_copy.c
+++ b/lib/asn1/gen_copy.c
@@ -91,11 +91,11 @@ void
 generate_type_copy (Symbol *s)
 {
   fprintf (headerfile,
-	   "void copy_%s(%s *, %s *);\n",
+	   "void copy_%s(const %s *, %s *);\n",
 	   s->gen_name, s->gen_name, s->gen_name);
 
   fprintf (codefile, "void\n"
-	   "copy_%s(%s *from, %s *to)\n"
+	   "copy_%s(const %s *from, %s *to)\n"
 	   "{\n",
 	   s->gen_name, s->gen_name, s->gen_name);