diff --git a/src/pal/pal_consts.h b/src/pal/pal_consts.h
index 8e32c61..5e14a7f 100644
--- a/src/pal/pal_consts.h
+++ b/src/pal/pal_consts.h
@@ -1,3 +1,5 @@
+#pragma once
+
 namespace snmalloc
 {
   /**