diff --git a/src/opt/opt_preprocess.cpp b/src/opt/opt_preprocess.cpp
index d3475fcb0..886d7fbb0 100644
--- a/src/opt/opt_preprocess.cpp
+++ b/src/opt/opt_preprocess.cpp
@@ -30,7 +30,6 @@ Notes:
 
 --*/
 
-#pragma once
 
 #include "opt/opt_preprocess.h"
 #include "util/max_cliques.h"