diff --git a/spec/section/expressions.md b/spec/section/expressions.md
index b3e419b..62eda26 100644
--- a/spec/section/expressions.md
+++ b/spec/section/expressions.md
@@ -10,7 +10,7 @@ An expression map (`rml:ExpressionMap`) is an abstract class, that is
* 0 or 1 `rml:template`, or
* another property, or properties, defined by a subclass of `rml:ExpressionMap`.
-Each of these properties specifies an [=expression=] which, upon evaluation, results in an ordered list of values, called the expression evaluation result.
+Each of these properties specifies an [=expression=] which, upon evaluation, results in a naturally ordered list of values (i.e., preserving the order in which they are produced by the iterations), called the expression evaluation result.
The reference expression set of an [=expression map=] is the set of expressions which are evaluated on a [=logical iteration=].