diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 2d75a7a506..e5ce553418 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -8,6 +8,8 @@
 #include <unistd.h>
 #include <signal.h>
 
+#include <iostream>
+
 
 namespace nix {