diff --git a/src/ui/common/Validators.hpp b/src/ui/common/Validators.hpp
index a7166e47..76e1b3a5 100644
--- a/src/ui/common/Validators.hpp
+++ b/src/ui/common/Validators.hpp
@@ -17,6 +17,8 @@
  * along with LMS.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#pragma once
+
 #include <Wt/WRegExpValidator>
 #include <Wt/WLengthValidator>