diff --git a/src/css.rs b/src/css.rs
index 8732367..e00b2da 100644
--- a/src/css.rs
+++ b/src/css.rs
@@ -100,7 +100,7 @@ impl Css {
                     self.idx = self.blocks.len() + 1;
                     self.inner_rulesets = 0;
                     self.blocks
-                        .push(Toplevel::new_rule(super_selector.zip(selector)));
+                        .push(Toplevel::new_rule(super_selector.zip(&selector)));
                     for rule in rules {
                         self.at_root = true;
                         self.parse_stmt(rule);
@@ -111,7 +111,7 @@ impl Css {
                     self.idx += 1;
                     self.at_root = false;
                     self.blocks
-                        .push(Toplevel::new_rule(super_selector.zip(selector)));
+                        .push(Toplevel::new_rule(super_selector.zip(&selector)));
                     for rule in rules {
                         self.parse_stmt(rule);
                     }
diff --git a/src/format.rs b/src/format.rs
index 568f3eb..c3c7d07 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -58,12 +58,7 @@ impl<W: Write> PrettyPrinter<W> {
                 rules,
                 super_selector,
             }) => {
-                writeln!(
-                    self.buf,
-                    "{}{} {{",
-                    padding,
-                    super_selector.clone().zip(selector.clone())
-                )?;
+                writeln!(self.buf, "{}{} {{", padding, super_selector.zip(selector))?;
                 self.scope += 1;
                 for rule in rules {
                     self.pretty_print_stmt(rule)?;
diff --git a/src/main.rs b/src/main.rs
index be51a5a..9f3312e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -405,7 +405,7 @@ impl<'a> StyleSheetParser<'a> {
                 }
                 Expr::Selector(s) => {
                     self.scope += 1;
-                    let rules = self.eat_rules(&super_selector.clone().zip(s.clone()), scope);
+                    let rules = self.eat_rules(&super_selector.zip(&s), scope);
                     stmts.push(Stmt::RuleSet(RuleSet {
                         super_selector: super_selector.clone(),
                         selector: s,
@@ -634,7 +634,7 @@ pub(crate) fn eat_expr<I: Iterator<Item = Token>>(
 /// Functions that print to stdout or stderr
 impl<'a> StyleSheetParser<'a> {
     fn debug(&self, pos: Pos, message: &str) {
-        println!("{}:{} Debug: {}", self.file, pos.line(), message);
+        eprintln!("{}:{} Debug: {}", self.file, pos.line(), message);
     }
 
     fn warn(&self, pos: Pos, message: &str) {
diff --git a/src/mixin.rs b/src/mixin.rs
index 1139c91..e4a821c 100644
--- a/src/mixin.rs
+++ b/src/mixin.rs
@@ -115,7 +115,7 @@ impl Mixin {
                 Expr::Include(_) | Expr::MixinDecl(_, _) => todo!(),
                 Expr::Selector(s) => {
                     self.nesting += 1;
-                    let rules = self.eval(&super_selector.clone().zip(s.clone()), scope)?;
+                    let rules = self.eval(&super_selector.zip(&s), scope)?;
                     stmts.push(Stmt::RuleSet(RuleSet {
                         super_selector: super_selector.clone(),
                         selector: s,
diff --git a/src/selector.rs b/src/selector.rs
index 1cc3d78..812f2be 100644
--- a/src/selector.rs
+++ b/src/selector.rs
@@ -268,29 +268,27 @@ impl Selector {
         SelectorParser::new(scope).all_selectors(tokens)
     }
 
-    pub fn zip(self, other: Selector) -> Selector {
+    pub fn zip(&self, other: &Selector) -> Selector {
         if self.0.is_empty() {
-            return Selector(other.0);
+            return Selector(other.0.clone());
         }
         let mut rules: Vec<SelectorKind> = Vec::with_capacity(self.0.len() + other.0.len());
-        let sel1_split: Vec<Vec<SelectorKind>> = self
+        let sel1_split: Vec<&[SelectorKind]> =
+            self.0.split(|sel| sel == &SelectorKind::Multiple).collect();
+        let sel2_split: Vec<&[SelectorKind]> = other
             .0
             .split(|sel| sel == &SelectorKind::Multiple)
-            .map(|x| x.to_vec())
             .collect();
-        let sel2_split: Vec<Vec<SelectorKind>> = other
-            .0
-            .split(|sel| sel == &SelectorKind::Multiple)
-            .map(|x| x.to_vec())
-            .collect();
-        for (idx, sel1) in sel1_split.iter().enumerate() {
+        let len1 = sel1_split.len();
+        let len2 = sel2_split.len();
+        for (idx, sel1) in sel1_split.into_iter().enumerate() {
             for (idx2, sel2) in sel2_split.iter().enumerate() {
-                let mut this_selector = Vec::with_capacity(other.0.len());
+                let mut this_selector: Vec<SelectorKind> = Vec::with_capacity(other.0.len());
                 let mut found_super = false;
 
-                for sel in sel2 {
+                for sel in *sel2 {
                     if sel == &SelectorKind::Super {
-                        this_selector.extend(sel1.iter().cloned());
+                        this_selector.extend(sel1.to_vec());
                         found_super = true;
                     } else {
                         this_selector.push(sel.clone());
@@ -298,12 +296,12 @@ impl Selector {
                 }
 
                 if !found_super {
-                    rules.extend(sel1.iter().cloned());
+                    rules.extend(sel1.to_vec());
                     rules.push(SelectorKind::Whitespace);
                 }
                 rules.extend(this_selector);
 
-                if !(idx + 1 == sel1_split.len() && idx2 + 1 == sel2_split.len()) {
+                if !(idx + 1 == len1 && idx2 + 1 == len2) {
                     rules.push(SelectorKind::Multiple);
                 }
             }