diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index f3e8a34bd..eac53b894 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -7,6 +7,7 @@
 #include "hash.hh"
 #include "config.hh"
 
+#include <regex>
 #include <map>
 #include <optional>
 #include <unordered_map>