diff --git a/src/CalcManager/Ratpack/CalcErr.h b/src/CalcManager/Ratpack/CalcErr.h
index 80b7229c..8c23e440 100644
--- a/src/CalcManager/Ratpack/CalcErr.h
+++ b/src/CalcManager/Ratpack/CalcErr.h
@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+#pragma once
+
 // CalcErr.h
 //
 // Defines the error codes thrown by ratpak and caught by Calculator