diff --git a/src/libexpr/include/nix/expr/attr-set.hh b/src/libexpr/include/nix/expr/attr-set.hh
index 283786f4d..c44e8a6b9 100644
--- a/src/libexpr/include/nix/expr/attr-set.hh
+++ b/src/libexpr/include/nix/expr/attr-set.hh
@@ -23,7 +23,7 @@ struct Attr
        way we keep Attr size at two words with no wasted space. */
     Symbol name;
     PosIdx pos;
-    Value * value;
+    Value * value = nullptr;
     Attr(Symbol name, Value * value, PosIdx pos = noPos)
         : name(name), pos(pos), value(value) { };
     Attr() { };