diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
index 8ba0f38..691c791 100644
--- a/include/crypto/pkcs7.h
+++ b/include/crypto/pkcs7.h
@@ -9,6 +9,7 @@
  * 2 of the Licence, or (at your option) any later version.
  */
 
+struct key;
 struct pkcs7_message;
 
 /*
@@ -23,6 +24,13 @@
 				  bool want_wrapper);
 
 /*
+ * pkcs7_trust.c
+ */
+extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
+				struct key *trust_keyring,
+				bool *_trusted);
+
+/*
  * pkcs7_verify.c
  */
 extern int pkcs7_verify(struct pkcs7_message *pkcs7);