diff --git a/src/mem/slowalloc.h b/src/mem/slowalloc.h
index 0ab1169..87be4d1 100644
--- a/src/mem/slowalloc.h
+++ b/src/mem/slowalloc.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "globalalloc.h"
 
 namespace snmalloc