diff --git a/proto/substrait/algebra.proto b/proto/substrait/algebra.proto
index 9fec02a9f..37ba42600 100644
--- a/proto/substrait/algebra.proto
+++ b/proto/substrait/algebra.proto
@@ -819,9 +819,12 @@ message Expression {
       UserDefined user_defined = 33;
     }
 
-    // whether the literal type should be treated as a nullable type. Applies to
-    // all members of union other than the Typed null (which should directly
-    // declare nullability).
+    // Whether the literal_type above should be treated as a nullable type.
+    // Applies to all members of the literal_type oneof EXCEPT:
+    //  * Type null
+    //  * Type.List empty_list
+    //  * Type.Map empty_map
+    // which should declare their nullability directly instead.
     bool nullable = 50;
 
     // optionally points to a type_variation_anchor defined in this plan.