diff --git a/src/polyxx/rational_interval.cpp b/src/polyxx/rational_interval.cpp
index 9983e69..d365d91 100644
--- a/src/polyxx/rational_interval.cpp
+++ b/src/polyxx/rational_interval.cpp
@@ -1,6 +1,7 @@
 #include "polyxx/rational_interval.h"
 
 #include <cassert>
+#include <iostream>
 
 namespace poly {