diff --git a/Modular_arithmetic/examples/Modular_arithmetic/modular_filter.cpp b/Modular_arithmetic/examples/Modular_arithmetic/modular_filter.cpp
index 324d58adb95..0155cc0c867 100644
--- a/Modular_arithmetic/examples/Modular_arithmetic/modular_filter.cpp
+++ b/Modular_arithmetic/examples/Modular_arithmetic/modular_filter.cpp
@@ -1,4 +1,5 @@
 #include <CGAL/config.h>
+#include <iostream>
 
 #ifdef CGAL_USE_GMP