diff --git a/lib/src/parser.dart b/lib/src/parser.dart
index 491c2a67..6acd2cb7 100644
--- a/lib/src/parser.dart
+++ b/lib/src/parser.dart
@@ -387,8 +387,8 @@ class Parser {
     if (first == $plus || first == $minus) _scanner.readChar();
 
     num number = 0;
-    var first = _scanner.peekChar();
-    if (!isDigit(first) && first != $dot) _scanner.error("Expected number.");
+    var second = _scanner.peekChar();
+    if (!isDigit(second) && second != $dot) _scanner.error("Expected number.");
 
     while (isDigit(_scanner.peekChar())) {
       number *= 10;
@@ -469,7 +469,7 @@ class Parser {
       }
     }
 
-    return buffer.interpolation(_scanner.spanFrom(start));
+    return new StringExpression(buffer.interpolation(_scanner.spanFrom(start)));
   }
 
   Expression _hexColor() => throw new UnimplementedError();
diff --git a/lib/src/visitor/css/serialize.dart b/lib/src/visitor/css/serialize.dart
index 6c1c0ef6..2be0c73c 100644
--- a/lib/src/visitor/css/serialize.dart
+++ b/lib/src/visitor/css/serialize.dart
@@ -6,11 +6,10 @@ import 'package:charcode/charcode.dart';
 
 import '../../ast/css/node.dart';
 import '../../util/character.dart';
-import '../../utils.dart';
 import '../../value.dart';
 import '../css.dart';
 
-String toCss(AstNode node) {
+String toCss(CssNode node) {
   var visitor = new _SerializeCssVisitor();
   node.accept(visitor);
   var result = visitor._buffer.toString();
@@ -68,10 +67,11 @@ class _SerializeCssVisitor extends CssVisitor {
     _buffer.writeCharCode($semicolon);
   }
 
-  void visitBoolean(SassBoolean value) => value.value.toString();
+  void visitBoolean(SassBoolean value) =>
+      _buffer.write(value.value.toString());
 
   void visitIdentifier(SassIdentifier value) =>
-      value.text.replaceAll("\n", " ");
+      _buffer.write(value.text.replaceAll("\n", " "));
 
   void visitList(SassList value) {
     if (value.contents.isEmpty) throw "() isn't a valid CSS value";
@@ -152,13 +152,6 @@ class _SerializeCssVisitor extends CssVisitor {
     return doubleQuote ? '"$buffer"' : "'$buffer'";
   }
 
-  num _round(num number) {
-    if (number is double && (number.isInfinite || number.isNaN)) return number;
-    if (almostEquals(number % 1, 0.0)) return number.round();
-    return (number * 10 * SassNumber.precision).round() /
-        (10 * SassNumber.precision);
-  }
-
   void _writeIndentation() {
     for (var i = 0; i < _indentation; i++) {
       _buffer.writeCharCode($space);
diff --git a/lib/src/visitor/sass/statement/perform.dart b/lib/src/visitor/sass/statement/perform.dart
index 5004669f..487215fa 100644
--- a/lib/src/visitor/sass/statement/perform.dart
+++ b/lib/src/visitor/sass/statement/perform.dart
@@ -43,16 +43,17 @@ class PerformVisitor extends StatementVisitor {
 
   void visitDeclaration(Declaration node) {
     var name = _performInterpolation(node.name);
-    var value = _performExpression(node.value);
+    var cssValue = _performExpression(node.value);
+    var value = cssValue.value;
 
     // Don't abort for an empty list because converting it to CSS will throw an
     // error that we want to user to see.
-    if (value.value.isBlank &&
-        !(value.value is SassList && value.value.contents.isEmpty)) {
+    if (value.isBlank &&
+        !(value is SassList && value.contents.isEmpty)) {
       return;
     }
 
-    _addChild(new CssDeclaration(name, value, span: node.span));
+    _addChild(new CssDeclaration(name, cssValue, span: node.span));
   }
 
   void visitStyleRule(StyleRule node) {