diff --git a/src/commands.hxx b/src/commands.hxx
index 1f3185c..fa6ec2f 100644
--- a/src/commands.hxx
+++ b/src/commands.hxx
@@ -1421,7 +1421,8 @@ class Certificate: public Command {
       Logger log(this, script);
       QString filename(script->replacevars(_filename));
       QFile cacertfile(filename);
-      if (!cacertfile.exists()) throw FileNotFound(filename);
+      if (!cacertfile.exists() || !cacertfile.open(QIODevice::ReadOnly))
+        throw FileNotFound(filename);
       QSslCertificate cacert(&cacertfile);
       if (cacert.isNull()) throw NotACertificate(filename);
       QSslSocket::addDefaultCaCertificate(cacert);