diff --git a/source/lex.tex b/source/lex.tex
index bfd55be51d..3f579a351b 100644
--- a/source/lex.tex
+++ b/source/lex.tex
@@ -901,14 +901,16 @@
 \begin{bnf}
 \nontermdef{identifier-start}\br
     nondigit\br
-    \textnormal{an element of the translation character set with the Unicode property XID_Start}
+    \textnormal%
+	{an element of the translation character set with the Unicode property XID_Start or the Unicode property ID_Compat_Math_Start}
 \end{bnf}
 
 \begin{bnf}
 \nontermdef{identifier-continue}\br
     digit\br
     nondigit\br
-    \textnormal{an element of the translation character set with the Unicode property XID_Continue}
+    \textnormal%
+	{an element of the translation character set with the Unicode property XID_Continue or the Unicode property ID_Compat_Math_Continue}
 \end{bnf}
 
 \begin{bnf}
diff --git a/source/uax31.tex b/source/uax31.tex
index 79f0f7d0e9..6a13e10464 100644
--- a/source/uax31.tex
+++ b/source/uax31.tex
@@ -31,15 +31,17 @@
 where \tcode{<Start>} has the XID_Start property,
 \tcode{<Continue>} has the XID_Continue property, and
 \tcode{<Medial>} is a list of characters permitted between continue characters.
-For \Cpp{} we add the character \unicode{005f}{low line}, or \tcode{_},
-to the set of permitted \tcode{<Start>} characters,
-the \tcode{<Medial>} set is empty, and
-the \tcode{<Continue>} characters are unmodified.
+\UAX{31} also specifies some standard profiles,
+including the Mathematical Compatability Notation profile.
+For \Cpp{} we apply the Mathematical Compatability Notation profile,
+and we add the character \unicode{005f}{low line}, or \tcode{_},
+to the set of permitted \tcode{<Start>} characters.
+The \tcode{<Medial>} set is empty.
 In the grammar used in \UAX{31}, this is
 \begin{outputblock}
 <Identifier> := <Start> <Continue>*
-<Start> := XID_Start + @\textrm{\ucode{005f}}@
-<Continue> := <Start> + XID_Continue
+<Start> := XID_Start + ID_Compat_Math_Start + @\textrm{\ucode{005f}}@
+<Continue> := <Start> + XID_Continue + ID_Compat_Math_Continue
 \end{outputblock}
 
 \pnum