diff --git a/src/libstore/references.cc b/src/libstore/references.cc
index 68d1cbfbfb..a6f6e85fc8 100644
--- a/src/libstore/references.cc
+++ b/src/libstore/references.cc
@@ -4,6 +4,7 @@
 #include "archive.hh"
 
 #include <map>
+#include <cstdlib>
 
 
 namespace nix {