diff --git a/libsolutil/LinearExpression.h b/libsolutil/LinearExpression.h
index add117f1a..b4616e536 100644
--- a/libsolutil/LinearExpression.h
+++ b/libsolutil/LinearExpression.h
@@ -24,6 +24,8 @@
 #include <libsolutil/StringUtils.h>
 #include <liblangutil/Exceptions.h>
 
+#include <boost/rational.hpp>
+
 #include <range/v3/view/tail.hpp>
 #include <range/v3/algorithm/all_of.hpp>