diff --git a/src/token/RightParenthesis.java b/src/token/RightParenthesis.java
index 99829c5..8c15054 100644
--- a/src/token/RightParenthesis.java
+++ b/src/token/RightParenthesis.java
@@ -22,7 +22,7 @@ public class RightParenthesis extends Token {
     }
 
     @Override
-    public TailCall<SExpression> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
+    public TailCall<Cons> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
         return done(accumulator);
     }
 
diff --git a/src/token/Token.java b/src/token/Token.java
index b5808d8..0f7c833 100644
--- a/src/token/Token.java
+++ b/src/token/Token.java
@@ -40,12 +40,12 @@ public abstract class Token {
     public abstract SExpression parseSExpression(Supplier<Token> getNextToken);
 
     public SExpression parseSExpressionTail(Supplier<Token> getNextToken) {
-        Cons list = (Cons) parseListBackwards(NIL, getNextToken).invoke();
+        Cons list = parseListBackwards(NIL, getNextToken).invoke();
 
         return reverse(NIL, list).invoke();
     }
 
-    public TailCall<SExpression> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
+    public TailCall<Cons> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
         Cons nextAccumulator = new Cons(parseSExpression(getNextToken), accumulator);
         Token next = getNextToken.get();