diff --git a/Doc/lib/libsocket.tex b/Doc/lib/libsocket.tex
index 6096391..4470ce5 100644
--- a/Doc/lib/libsocket.tex
+++ b/Doc/lib/libsocket.tex
@@ -107,6 +107,8 @@
 representing an error returned by a library call.
 \var{string} represents the description of \var{error}, as returned
 by the \cfunction{gai_strerror()} C function.
+The \var{error} value will match one of the \constant{EAI_*} constants
+defined in this module.
 \end{excdesc}
 
 \begin{excdesc}{timeout}