diff --git a/libasn1fix/asn1fix_misc.h b/libasn1fix/asn1fix_misc.h
index e88e432..a586faa 100644
--- a/libasn1fix/asn1fix_misc.h
+++ b/libasn1fix/asn1fix_misc.h
@@ -44,4 +44,9 @@
  */
 int asn1f_count_children(asn1p_expr_t *parent);
 
+/*
+ * Check if type is explicitly known.
+ */
+int asn1f_check_known_external_type(const char *);
+
 #endif	/* _ASN1FIX_MISC_H_ */