diff --git a/pkgs/intl_translation/lib/src/messages/composite_message.dart b/pkgs/intl_translation/lib/src/messages/composite_message.dart
index 76191947..a3a66eb4 100644
--- a/pkgs/intl_translation/lib/src/messages/composite_message.dart
+++ b/pkgs/intl_translation/lib/src/messages/composite_message.dart
@@ -23,6 +23,6 @@ class CompositeMessage extends Message {
   String toString() => 'CompositeMessage($pieces)';
   @override
   String expanded(
-          [String Function(dynamic, dynamic) transform = nullTransform]) =>
+          [String Function(Message, Object) transform = nullTransform]) =>
       pieces.map((chunk) => transform(this, chunk)).join('');
 }
diff --git a/pkgs/intl_translation/lib/src/messages/literal_string_message.dart b/pkgs/intl_translation/lib/src/messages/literal_string_message.dart
index 9ad56c54..f5343818 100644
--- a/pkgs/intl_translation/lib/src/messages/literal_string_message.dart
+++ b/pkgs/intl_translation/lib/src/messages/literal_string_message.dart
@@ -16,6 +16,6 @@ class LiteralString extends Message {
   String toString() => 'Literal($string)';
   @override
   String expanded(
-          [String Function(dynamic, dynamic) transform = nullTransform]) =>
+          [String Function(Message, Object) transform = nullTransform]) =>
       transform(this, string);
 }
diff --git a/pkgs/intl_translation/lib/src/messages/main_message.dart b/pkgs/intl_translation/lib/src/messages/main_message.dart
index fbc7ff88..9943fde1 100644
--- a/pkgs/intl_translation/lib/src/messages/main_message.dart
+++ b/pkgs/intl_translation/lib/src/messages/main_message.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
+
 import 'complex_message.dart';
 import 'message.dart';
 import 'message_extraction_exception.dart';
@@ -121,7 +122,7 @@ class MainMessage extends ComplexMessage {
   /// See [messagePieces].
   @override
   String expanded(
-          [String Function(Message, dynamic) transform = nullTransform]) =>
+          [String Function(Message, Object) transform = nullTransform]) =>
       messagePieces.map((chunk) => transform(this, chunk)).join('');
 
   /// Record the translation for this message in the given locale, after
diff --git a/pkgs/intl_translation/lib/src/messages/message.dart b/pkgs/intl_translation/lib/src/messages/message.dart
index 81fcbb9c..e66bdf34 100644
--- a/pkgs/intl_translation/lib/src/messages/message.dart
+++ b/pkgs/intl_translation/lib/src/messages/message.dart
@@ -369,8 +369,8 @@ abstract class Message {
     return value;
   }
 
-  /// Expand this string out into a printed form. The function [f] will be
+  /// Expand this string out into a printed form. The function [transform] is
   /// applied to any sub-messages, allowing this to be used to generate a form
   /// suitable for a wide variety of translation file formats.
-  String expanded([String Function(dynamic, dynamic) transform]);
+  String expanded([String Function(Message, Object) transform]);
 }
diff --git a/pkgs/intl_translation/lib/src/messages/pair_message.dart b/pkgs/intl_translation/lib/src/messages/pair_message.dart
index 74450861..03896c78 100644
--- a/pkgs/intl_translation/lib/src/messages/pair_message.dart
+++ b/pkgs/intl_translation/lib/src/messages/pair_message.dart
@@ -12,7 +12,7 @@ class PairMessage<T extends Message, S extends Message> extends Message {
 
   @override
   String expanded(
-          [String Function(dynamic, dynamic) transform = nullTransform]) =>
+          [String Function(Message, Object) transform = nullTransform]) =>
       [first, second].map((chunk) => transform(this, chunk)).join('');
 
   @override
diff --git a/pkgs/intl_translation/lib/src/messages/submessages/submessage.dart b/pkgs/intl_translation/lib/src/messages/submessages/submessage.dart
index 8391804f..a6a20bd3 100644
--- a/pkgs/intl_translation/lib/src/messages/submessages/submessage.dart
+++ b/pkgs/intl_translation/lib/src/messages/submessages/submessage.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
+
 import '../complex_message.dart';
 import '../composite_message.dart';
 import '../literal_string_message.dart';
@@ -59,9 +60,9 @@ abstract class SubMessage extends ComplexMessage {
 
   @override
   String expanded(
-      [String Function(dynamic, dynamic) transform = nullTransform]) {
+      [String Function(Message, Object) transform = nullTransform]) {
     String fullMessageForClause(String key) =>
-        '$key{${transform(parent, this[key])}}';
+        '$key{${transform(parent!, this[key])}}';
     var clauses = attributeNames
         .where((key) => this[key] != null)
         .map(fullMessageForClause)
diff --git a/pkgs/intl_translation/lib/src/messages/variable_substitution_message.dart b/pkgs/intl_translation/lib/src/messages/variable_substitution_message.dart
index acc56e55..d7ef572e 100644
--- a/pkgs/intl_translation/lib/src/messages/variable_substitution_message.dart
+++ b/pkgs/intl_translation/lib/src/messages/variable_substitution_message.dart
@@ -62,6 +62,6 @@ class VariableSubstitution extends Message {
   String toString() => 'VariableSubstitution(${index ?? _variableName})';
   @override
   String expanded(
-          [String Function(dynamic, dynamic) transform = nullTransform]) =>
-      transform(this, index);
+          [String Function(Message, Object) transform = nullTransform]) =>
+      transform(this, index!);
 }