diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 70ee354e50..8413819114 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -82,7 +82,6 @@ using std::map;
 
 /* Forward definition. */
 class Worker;
-struct Agent;
 
 
 /* A pointer to a goal. */