diff --git a/book.tex b/book.tex
index 9ad0cae..60e9c3d 100644
--- a/book.tex
+++ b/book.tex
@@ -2163,7 +2163,7 @@ \subsection{Extensible Interpreters via Method Overriding}
 \end{minipage}
 \begin{minipage}{0.45\textwidth}
   \begin{lstlisting}
-def InterpLvar(InterpLint):
+class InterpLvar(InterpLint):
   def interp_exp(e):
     match e:
       case Name(id):