diff --git a/poppler/SignatureHandler.cc b/poppler/SignatureHandler.cc
index 10caed7..64f2d4d 100644
--- a/poppler/SignatureHandler.cc
+++ b/poppler/SignatureHandler.cc
@@ -322,6 +322,7 @@ CertificateValidationStatus SignatureHandler::NSS_CertTranslate(SECErrorCodes ns
   switch(nss_code)
   {
     case SEC_ERROR_UNKNOWN_ISSUER:
+    case SEC_ERROR_UNTRUSTED_ISSUER:
       return CERTIFICATE_UNTRUSTED;
 
     case SEC_ERROR_REVOKED_CERTIFICATE: