diff --git a/src/tools/json/JsonValidator.h b/src/tools/json/JsonValidator.h
index 8f424ac2..745e608c 100644
--- a/src/tools/json/JsonValidator.h
+++ b/src/tools/json/JsonValidator.h
@@ -22,6 +22,7 @@ along with OpenOCPP. If not, see <http://www.gnu.org/licenses/>.
 #include "json.h"
 
 #include <memory>
+#include <string>
 
 namespace ocpp
 {