diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index d0c75a82a..ef4ea3706 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -17,6 +17,8 @@
 #include <signal.h>
 #include <spawn.h>
 
+extern char * * environ;
+
 
 namespace nix {