diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index 0e3439b..b822e6c 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -2315,7 +2315,7 @@
 that `a == e`.
 
 ```
-// Config            Evaluates to
+// Config            Evaluates to (requiring concrete values)
 x: {                  x: {
     a: b + 100            a: _|_ // cycle detected
     b: a - 100            b: _|_ // cycle detected