diff --git a/src/sqlast/mod.rs b/src/sqlast/mod.rs
index c5e85c09..1461726d 100644
--- a/src/sqlast/mod.rs
+++ b/src/sqlast/mod.rs
@@ -76,7 +76,7 @@ pub enum ASTNode {
     },
     /// A parenthesized subquery `(SELECT ...)`, used in expression like
     /// `SELECT (subquery) AS x` or `WHERE (subquery) = x`
-    SQLSubquery(SQLSelect),
+    SQLSubquery(Box<SQLSelect>),
 }
 
 impl ToString for ASTNode {
diff --git a/src/sqlast/query.rs b/src/sqlast/query.rs
index 385173a1..887042f9 100644
--- a/src/sqlast/query.rs
+++ b/src/sqlast/query.rs
@@ -6,18 +6,18 @@ pub struct SQLSelect {
     pub projection: Vec<ASTNode>,
     /// FROM
     pub relation: Option<TableFactor>,
-    // JOIN
+    /// JOIN
     pub joins: Vec<Join>,
     /// WHERE
-    pub selection: Option<Box<ASTNode>>,
+    pub selection: Option<ASTNode>,
     /// ORDER BY
     pub order_by: Option<Vec<SQLOrderByExpr>>,
     /// GROUP BY
     pub group_by: Option<Vec<ASTNode>>,
     /// HAVING
-    pub having: Option<Box<ASTNode>>,
+    pub having: Option<ASTNode>,
     /// LIMIT
-    pub limit: Option<Box<ASTNode>>,
+    pub limit: Option<ASTNode>,
 }
 
 impl ToString for SQLSelect {
@@ -37,7 +37,7 @@ impl ToString for SQLSelect {
             s += &join.to_string();
         }
         if let Some(ref selection) = self.selection {
-            s += &format!(" WHERE {}", selection.as_ref().to_string());
+            s += &format!(" WHERE {}", selection.to_string());
         }
         if let Some(ref group_by) = self.group_by {
             s += &format!(
@@ -50,7 +50,7 @@ impl ToString for SQLSelect {
             );
         }
         if let Some(ref having) = self.having {
-            s += &format!(" HAVING {}", having.as_ref().to_string());
+            s += &format!(" HAVING {}", having.to_string());
         }
         if let Some(ref order_by) = self.order_by {
             s += &format!(
@@ -63,7 +63,7 @@ impl ToString for SQLSelect {
             );
         }
         if let Some(ref limit) = self.limit {
-            s += &format!(" LIMIT {}", limit.as_ref().to_string());
+            s += &format!(" LIMIT {}", limit.to_string());
         }
         s
     }
diff --git a/src/sqlparser.rs b/src/sqlparser.rs
index b72e8fbc..f2d616cc 100644
--- a/src/sqlparser.rs
+++ b/src/sqlparser.rs
@@ -197,7 +197,7 @@ impl Parser {
                 }
                 Token::LParen => {
                     let expr = if self.parse_keyword("SELECT") {
-                        ASTNode::SQLSubquery(self.parse_select()?)
+                        ASTNode::SQLSubquery(Box::new(self.parse_select()?))
                     } else {
                         ASTNode::SQLNested(Box::new(self.parse_expr()?))
                     };
@@ -1129,7 +1129,7 @@ impl Parser {
 
         let selection = if self.parse_keyword("WHERE") {
             let expr = self.parse_expr()?;
-            Some(Box::new(expr))
+            Some(expr)
         } else {
             None
         };
@@ -1141,7 +1141,7 @@ impl Parser {
         };
 
         let having = if self.parse_keyword("HAVING") {
-            Some(Box::new(self.parse_expr()?))
+            Some(self.parse_expr()?)
         } else {
             None
         };
@@ -1374,12 +1374,12 @@ impl Parser {
     }
 
     /// Parse a LIMIT clause
-    pub fn parse_limit(&mut self) -> Result<Option<Box<ASTNode>>, ParserError> {
+    pub fn parse_limit(&mut self) -> Result<Option<ASTNode>, ParserError> {
         if self.parse_keyword("ALL") {
             Ok(None)
         } else {
             self.parse_literal_int()
-                .map(|n| Some(Box::new(ASTNode::SQLValue(Value::Long(n)))))
+                .map(|n| Some(ASTNode::SQLValue(Value::Long(n))))
         }
     }
 }
diff --git a/tests/sqlparser_generic.rs b/tests/sqlparser_generic.rs
index 3921ea60..0d613469 100644
--- a/tests/sqlparser_generic.rs
+++ b/tests/sqlparser_generic.rs
@@ -54,7 +54,7 @@ fn parse_simple_select() {
             projection, limit, ..
         }) => {
             assert_eq!(3, projection.len());
-            assert_eq!(Some(Box::new(ASTNode::SQLValue(Value::Long(5)))), limit);
+            assert_eq!(Some(ASTNode::SQLValue(Value::Long(5))), limit);
         }
         _ => assert!(false),
     }
@@ -207,7 +207,7 @@ fn parse_like() {
                         "%a".to_string()
                     ))),
                 },
-                *selection.unwrap()
+                selection.unwrap()
             );
         }
         _ => assert!(false),
@@ -227,7 +227,7 @@ fn parse_not_like() {
                         "%a".to_string()
                     ))),
                 },
-                *selection.unwrap()
+                selection.unwrap()
             );
         }
         _ => assert!(false),
@@ -287,7 +287,7 @@ fn parse_select_order_by_limit() {
                 ]),
                 order_by
             );
-            assert_eq!(Some(Box::new(ASTNode::SQLValue(Value::Long(2)))), limit);
+            assert_eq!(Some(ASTNode::SQLValue(Value::Long(2))), limit);
         }
         _ => assert!(false),
     }