diff --git a/src/main/java/org/sablecc/sablecc/lexer/Lexer.java b/src/main/java/org/sablecc/sablecc/lexer/Lexer.java
index be9622ad4ae79cc1b9f795441bed0c8036cff592..bb0f9ff3e44008698a0869b4692cdce1b6698dbd 100644
--- a/src/main/java/org/sablecc/sablecc/lexer/Lexer.java
+++ b/src/main/java/org/sablecc/sablecc/lexer/Lexer.java
@@ -20,7 +20,7 @@ public class Lexer
     protected Token token;
     protected State state = State.NORMAL;
 
-    private PushbackReader in;
+    private final PushbackReader in;
     protected int line;
     protected int pos;
     private boolean cr;
diff --git a/src/main/resources/org/sablecc/sablecc/lexer.txt b/src/main/resources/org/sablecc/sablecc/lexer.txt
index d1d3fdec95d45944f72b3b99d14d438bf607eeed..d441b05d32d84180ba5591471048cbeadb56dd5e 100644
--- a/src/main/resources/org/sablecc/sablecc/lexer.txt
+++ b/src/main/resources/org/sablecc/sablecc/lexer.txt
@@ -44,7 +44,7 @@ public class Lexer
     protected Token token;
     protected State state = State.$1$;
 
-    private PushbackReader in;
+    private final PushbackReader in;
     protected int line;
     protected int pos;
     private boolean cr;