diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index cbd1efd..e5f8a66 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -5,6 +5,10 @@ include(UseJava)
 
 project(Lox NONE)
 
+add_custom_command(OUTPUT com/craftinginterpreters/lox/Expr.java
+  COMMAND java -jar GenerateAst.jar com/craftinginterpreters/lox
+  DEPENDS GenerateAst)
+
 add_jar(Lox
   com/craftinginterpreters/lox/Lox.java
   com/craftinginterpreters/lox/TokenType.java