diff --git a/src/gn/value_extractors.cc b/src/gn/value_extractors.cc
index 9eb7593..3984d22 100644
--- a/src/gn/value_extractors.cc
+++ b/src/gn/value_extractors.cc
@@ -51,7 +51,7 @@
       return false;
     if (!dest->push_back(new_one)) {
       // Already in the list, throw error.
-      *err = Err(item, "Duplicate item in list");
+      *err = Err(item, "Duplicate item " + item.ToString(true) + " in list.");
       size_t previous_index = dest->IndexOf(new_one);
       err->AppendSubErr(
           Err(input_list[previous_index], "This was the previous definition."));