diff --git a/libyul/optimiser/Scoper.h b/libyul/optimiser/Scoper.h
index a5dd679a1..2e262117e 100644
--- a/libyul/optimiser/Scoper.h
+++ b/libyul/optimiser/Scoper.h
@@ -15,6 +15,8 @@
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
 // SPDX-License-Identifier: GPL-3.0
+#pragma once
+
 /**
  * Base class that assigns scope to Yul AST
  */