diff --git a/source/compatibility.tex b/source/compatibility.tex
index 8b5a3104da..c23122018c 100644
--- a/source/compatibility.tex
+++ b/source/compatibility.tex
@@ -1892,6 +1892,11 @@
 
 Subclause \ref{cwchar.syn} describes the changes.
 
+\pnum
+Header \tcode{<cstddef>}~(\ref{cstddef.syn})\indexlibrary{\idxhdr{cstddef}}
+declares the name \tcode{nullptr_t} in addition to the names declared in
+\tcode{<stddef.h>} in the C standard library.
+
 \rSec2[diff.mods.to.behavior]{Modifications to behavior}
 
 \pnum