diff --git a/source/iostreams.tex b/source/iostreams.tex
index 18a19fc2ed..24fcd1981a 100644
--- a/source/iostreams.tex
+++ b/source/iostreams.tex
@@ -7933,6 +7933,7 @@
 writes the character representation of
 formatting arguments provided by \tcode{args}
 formatted according to specifications given in \tcode{fmt} to \tcode{stream}.
+Then establishes an observable checkpoint\iref{intro.abstract}.
 
 \pnum
 \throws