diff --git a/source/intro.tex b/source/intro.tex
index 5cb98d2101..5179e1e580 100644
--- a/source/intro.tex
+++ b/source/intro.tex
@@ -860,6 +860,7 @@
 results in a contract violation\iref{structure.specifications}.
 
 \pnum
+\recommended
 An implementation is encouraged to document its limitations in
 the size or complexity of the programs it can successfully process,
 if possible and where known.