diff --git a/libasn1compiler/asn1c_save.c b/libasn1compiler/asn1c_save.c
index f302ceb..6a094f7 100644
--- a/libasn1compiler/asn1c_save.c
+++ b/libasn1compiler/asn1c_save.c
@@ -617,12 +617,16 @@
 
     abuf_printf(buf, "/*\n * Generated by asn1c-" VERSION
                      " (http://lionet.info/asn1c)\n */\n\n");
+    abuf_printf(buf,
+                "struct asn_TYPE_descriptor_s;\t"
+                "/* Forward declaration */\n\n");
+
 
     TQ_FOR(mod, &(arg->asn->modules), mod_next) {
         TQ_FOR(arg->expr, &(mod->members), next) {
             if(include_type_to_pdu_collection(arg) == TI_NOT_INCLUDED) continue;
             abuf_printf(buf,
-                        "extern asn_TYPE_descriptor_t "
+                        "extern struct asn_TYPE_descriptor_s "
                         "asn_DEF_%s;\n",
                         asn1c_make_identifier(0, arg->expr, NULL));
         }
@@ -724,10 +728,19 @@
 
 static int
 need_to_generate_pdu_collection(arg_t *arg) {
+    /* If -pdu=all or -pdu=auto are given, we need to generate one. */
 	if(arg->flags & (A1C_PDU_ALL|A1C_PDU_AUTO))
 		return 1;
-	if(arg->flags & A1C_PDU_TYPE)
-		return (pduTypes > 1) ? 1 : 0;
+
+    /*
+     * If no -pdu=... flags were given, need to do it, too,
+     * effectively producing -pdu=auto.
+     */
+    if(!(arg->flags & (A1C_PDU_ALL | A1C_PDU_AUTO | A1C_PDU_TYPE))) return 1;
+
+    if(arg->flags & A1C_PDU_TYPE) {
+        return (pduTypes > 1) ? 1 : 0;
+    }
 	return 0;
 }
 
@@ -757,7 +770,11 @@
     }
 
     if((arg->flags & A1C_PDU_ALL)
+       /* -pdu=auto */
        || ((arg->flags & A1C_PDU_AUTO) && !arg->expr->_type_referenced)
+       /* No -pdu=... whatsoever, act as if -pdu=auto */
+       || (!(arg->flags & (A1C_PDU_ALL | A1C_PDU_AUTO | A1C_PDU_TYPE))
+           && !arg->expr->_type_referenced)
        || asn1c__pdu_type_lookup(arg->expr->Identifier)) {
         return 1;
     }