diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 5ee6359a8..ce798ed96 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -20,10 +20,10 @@ namespace nix {
 
 /**
  * We put a limit on primop arity because it lets us use a fixed size array on
- * the stack. 16 is already an impractical number of arguments. Use an attrset
+ * the stack. 8 is already an impractical number of arguments. Use an attrset
  * argument for such overly complicated functions.
  */
-constexpr size_t maxPrimOpArity = 64;
+constexpr size_t maxPrimOpArity = 8;
 
 class Store;
 class EvalState;