diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index ab46b448c..e7915dd99 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -17,7 +17,7 @@
 namespace nix {
 
 
-struct Store;
+class Store;
 class EvalState;
 class StorePath;
 enum RepairFlag : bool;