diff --git a/src/str.hpp b/src/str.hpp
index 1f84f5da..e16fad00 100644
--- a/src/str.hpp
+++ b/src/str.hpp
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include "nonstd/span.hpp"
+
 #include <set>
 #include <string>
 #include <vector>