diff --git a/source/lex.tex b/source/lex.tex
index 8f8df12ed3..7e7b6d1bc2 100644
--- a/source/lex.tex
+++ b/source/lex.tex
@@ -1776,7 +1776,7 @@
 
 \begin{bnf}
 \nontermdef{d-char-sequence}\br
-    d-char\opt{d-char-sequence}
+    d-char \opt{d-char-sequence}
 \end{bnf}
 
 \begin{bnf}