diff --git a/lib/al/include/Library/Execute/ExecuteTablesImpl.h b/lib/al/include/Library/Execute/ExecuteTablesImpl.h
index 91ed9031..17db0d30 100644
--- a/lib/al/include/Library/Execute/ExecuteTablesImpl.h
+++ b/lib/al/include/Library/Execute/ExecuteTablesImpl.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "Library/Execute/ExecuteOrder.h"
 #include "Library/Execute/ExecuteTable.h"
 
diff --git a/src/System/GameDataHolder.h b/src/System/GameDataHolder.h
index 98df436e..d64ffa2f 100644
--- a/src/System/GameDataHolder.h
+++ b/src/System/GameDataHolder.h
@@ -1,8 +1,3 @@
-/**
- * @file GameDataHolder.h
- * @brief Holds scenario / game data.
- */
-
 #pragma once
 
 #include <prim/seadSafeString.h>
diff --git a/tools/check-format.py b/tools/check-format.py
index 58ce27a7..9c48414f 100755
--- a/tools/check-format.py
+++ b/tools/check-format.py
@@ -36,6 +36,9 @@ def common_newline_eof(c, path):
 
 # Header files
 
+def header_pragma_once(c, path):
+    CHECK(lambda a:a=="#pragma once", c.splitlines()[0], "Headers must start with \"#pragma once\"!", path)
+
 
 # Source files
 
@@ -49,6 +52,7 @@ def check_source(c, path):
 
 def check_header(c, path):
     common_newline_eof(c, path)
+    header_pragma_once(c, path)
 
 def check_file(file_str):
     file = open(file_str, mode="r")