diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index 727b661e1..b00a79b7f 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -189,7 +189,7 @@ static void fetch(EvalState & state, const Pos & pos, Value * * args, Value & v,
     std::optional<std::string> url;
     std::optional<Hash> expectedHash;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {