diff --git a/lib/asn1/gen_decode.c b/lib/asn1/gen_decode.c
index f94948063..7f64248cd 100644
--- a/lib/asn1/gen_decode.c
+++ b/lib/asn1/gen_decode.c
@@ -32,6 +32,7 @@
  */
 
 #include "gen_locl.h"
+#include "lex.h"
 
 RCSID("$Id$");
 
@@ -160,6 +161,14 @@ find_tag (const Type *t,
 	*tag = t->tag.tagvalue;
 	break;
     case TType: 
+	if ((t->symbol->stype == Stype && t->symbol->type == NULL)
+	    || t->symbol->stype == SUndefined) {
+	    error_message("%s is imported or still undefined, "
+			  " can't generate tag checking data in CHOICE "
+			  "without this information",
+			  t->symbol->name);
+	    exit(1);
+	}
 	find_tag(t->symbol->type, cl, ty, tag);
 	return;
     case TUTCTime: