diff --git a/redfish-core/lib/certificate_service.hpp b/redfish-core/lib/certificate_service.hpp
index 276e2ac..6fc5515 100644
--- a/redfish-core/lib/certificate_service.hpp
+++ b/redfish-core/lib/certificate_service.hpp
@@ -161,7 +161,7 @@
     CertificateFile& operator=(CertificateFile&&) = delete;
     CertificateFile(const std::string& certString)
     {
-        std::array<char, 20> dirTemplate = {'/', 't', 'm', 'p', '/', 'C',
+        std::array<char, 18> dirTemplate = {'/', 't', 'm', 'p', '/', 'C',
                                             'e', 'r', 't', 's', '.', 'X',
                                             'X', 'X', 'X', 'X', 'X', '\0'};
         char* tempDirectory = mkdtemp(dirTemplate.data());