diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index afd344286..6a50c9934 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2008,7 +2008,7 @@ void EvalState::createBaseEnv()
        language feature gets added.  It's not necessary to increase it
        when primops get added, because you can just use `builtins ?
        primOp' to check. */
-    mkInt(v, 4);
+    mkInt(v, 5);
     addConstant("__langVersion", v);
 
     // Miscellaneous