diff --git a/lib/collection.dart b/lib/collection.dart
index 2a6b23f..bdff7e0 100644
--- a/lib/collection.dart
+++ b/lib/collection.dart
@@ -18,7 +18,6 @@ library quiver.collection;
 import 'dart:collection';
 import 'dart:math';
 
-import 'package:quiver/core.dart';
 import 'package:quiver/iterables.dart';
 
 part 'src/bimap.dart';
diff --git a/lib/src/lru_map.dart b/lib/src/lru_map.dart
index 84d524c..9567e5f 100644
--- a/lib/src/lru_map.dart
+++ b/lib/src/lru_map.dart
@@ -64,7 +64,7 @@ class LinkedLruHashMap<K, V> implements LruMap<K, V> {
   LinkedLruHashMap._fromMap(this._entries, {int maximumSize})
       // This pattern is used instead of a default value because we want to
       // be able to respect null values coming in from MapCache.lru.
-      : _maximumSize = firstNonNull(maximumSize, _DEFAULT_MAXIMUM_SIZE);
+      : _maximumSize = maximumSize ?? _DEFAULT_MAXIMUM_SIZE;
 
   /// Adds all key-value pairs of [other] to this map.
   ///
diff --git a/pubspec.yaml b/pubspec.yaml
index c671b02..79077f3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -14,7 +14,7 @@ authors:
 description: A collection of collections classes for Dart.
 homepage: https://github.com/QuiverDart/quiver_collection
 environment:
-  sdk: '>=1.8.0 <2.0.0'
+  sdk: '>=1.12.0 <2.0.0'
 dependencies:
   quiver: '>=0.21.4 <0.22.0'
 dev_dependencies: