diff --git a/source/CAS/Client.php b/source/CAS/Client.php
index 9ebc16b9..2db06709 100644
--- a/source/CAS/Client.php
+++ b/source/CAS/Client.php
@@ -1919,8 +1919,8 @@ public function setCasServerCACert($cert, $validate_cn)
         if (gettype($validate_cn) != 'boolean') {
             throw new CAS_TypeMismatchException($validate_cn, '$validate_cn', 'boolean');
         }
-        if ( !file_exists($cert) && $this->_requestImplementation instanceof CAS_TestHarness_DummyRequest){
-            throw new CAS_InvalidArgumentException("Certificate file does not exist");
+        if ( !file_exists($cert) && $this->_requestImplementation !== 'CAS_TestHarness_DummyRequest'){
+            throw new CAS_InvalidArgumentException("Certificate file does not exist " . $this->_requestImplementation);
         }
         $this->_cas_server_ca_cert = $cert;
         $this->_cas_server_cn_validate = $validate_cn;