diff --git a/src/security/v2/validation-policy-config.cpp b/src/security/v2/validation-policy-config.cpp
index f6f6ed6..2d82079 100644
--- a/src/security/v2/validation-policy-config.cpp
+++ b/src/security/v2/validation-policy-config.cpp
@@ -227,7 +227,7 @@
     case 's':
       return time::seconds(refreshPeriod);
     default:
-      BOOST_THROW_EXCEPTION(Error(std::string("Bad refresh time unit: ") + unit));
+      BOOST_THROW_EXCEPTION(Error("Bad refresh time unit: "s + unit));
   }
 }