diff --git a/src/core/importer.h b/src/core/importer.h
index 57ac6a0..1985f60 100644
--- a/src/core/importer.h
+++ b/src/core/importer.h
@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <functional>
 #include <memory>
 #include <string>
 #include <vector>