diff --git a/CHANGELOG.md b/CHANGELOG.md
index d893d5c..13b020d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.0.1
+
+* Fix a fuzzy arrow type warning.
+
 ## 1.0.0
 
 * **Breaking change**: The `allowTrailingOptions` argument to `new
diff --git a/lib/src/arg_parser.dart b/lib/src/arg_parser.dart
index fd6cb9a..62c8276 100644
--- a/lib/src/arg_parser.dart
+++ b/lib/src/arg_parser.dart
@@ -88,9 +88,18 @@
       bool negatable: true,
       void callback(bool value),
       bool hide: false}) {
-    _addOption(name, abbr, help, null, null, null, defaultsTo, callback,
+    _addOption(
+        name,
+        abbr,
+        help,
+        null,
+        null,
+        null,
+        defaultsTo,
+        callback == null ? null : (value) => callback(value as bool),
         OptionType.FLAG,
-        negatable: negatable, hide: hide);
+        negatable: negatable,
+        hide: hide);
   }
 
   /// Defines a value-taking option. Throws an [ArgumentError] if:
diff --git a/pubspec.yaml b/pubspec.yaml
index f5ead67..00fc576 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: args
-version: 1.0.1-dev
+version: 1.0.1
 author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/args
 description: >