diff --git a/lib/src/ast/selector/type.dart b/lib/src/ast/selector/type.dart
index 84e0fcc5..d6ce3dfa 100644
--- a/lib/src/ast/selector/type.dart
+++ b/lib/src/ast/selector/type.dart
@@ -25,7 +25,7 @@ class TypeSelector extends SimpleSelector {
       if (unified == null) return null;
       return [unified]..addAll(compound.skip(1));
     } else {
-      return [this]..addAll(compound);
+      return <SimpleSelector>[this]..addAll(compound);
     }
   }
 
diff --git a/lib/src/functions.dart b/lib/src/functions.dart
index eedaf539..f8c633a4 100644
--- a/lib/src/functions.dart
+++ b/lib/src/functions.dart
@@ -979,6 +979,6 @@ CompoundSelector _prependParent(CompoundSelector compound) {
       ..addAll(compound.components.skip(1)));
   } else {
     return new CompoundSelector(
-        [new ParentSelector()]..addAll(compound.components));
+        <SimpleSelector>[new ParentSelector()]..addAll(compound.components));
   }
 }
diff --git a/lib/src/visitor/perform.dart b/lib/src/visitor/perform.dart
index 0480d109..2f1558ec 100644
--- a/lib/src/visitor/perform.dart
+++ b/lib/src/visitor/perform.dart
@@ -545,7 +545,7 @@ class PerformVisitor implements StatementVisitor, ExpressionVisitor<Value> {
     } else if (condition is SupportsNegation) {
       return "not ${_parenthesize(condition.condition)}";
     } else if (condition is SupportsInterpolation) {
-      return condition.expression.accept(this);
+      return condition.expression.accept(this).toString();
     } else if (condition is SupportsDeclaration) {
       return "(${condition.name.accept(this)}: ${condition.value.accept(this)})";
     } else {
diff --git a/lib/src/visitor/serialize.dart b/lib/src/visitor/serialize.dart
index 7794fabb..b3e2579d 100644
--- a/lib/src/visitor/serialize.dart
+++ b/lib/src/visitor/serialize.dart
@@ -184,7 +184,7 @@ class _SerializeCssVisitor
     while (!scanner.isDone && scanner.readChar() != $lf) {}
     if (scanner.isDone) return null;
 
-    var min = null;
+    int min;
     while (!scanner.isDone) {
       while (!scanner.isDone && scanner.scanChar($space)) {}
       if (scanner.isDone || scanner.scanChar($lf)) continue;