diff --git a/packages/pigeon/lib/java_generator.dart b/packages/pigeon/lib/java_generator.dart
index 9f1d307c37..1d3a1deb4c 100644
--- a/packages/pigeon/lib/java_generator.dart
+++ b/packages/pigeon/lib/java_generator.dart
@@ -56,7 +56,9 @@ void _writeHostApi(Indent indent, Api api) {
         argSignature.add('${method.argType} arg');
       }
       if (method.isAsynchronous) {
-        argSignature.add('Result<${method.returnType}> result');
+        final String returnType =
+            method.returnType == 'void' ? 'Void' : method.returnType;
+        argSignature.add('Result<$returnType> result');
       }
       indent.writeln('$returnType ${method.name}(${argSignature.join(', ')});');
     }
@@ -94,9 +96,11 @@ void _writeHostApi(Indent indent, Api api) {
                   methodArgument.add('input');
                 }
                 if (method.isAsynchronous) {
+                  final String resultValue =
+                      method.returnType == 'void' ? 'null' : 'result.toMap()';
                   methodArgument.add(
                     'result -> { '
-                    'wrapped.put("${Keys.result}", result.toMap()); '
+                    'wrapped.put("${Keys.result}", $resultValue); '
                     'reply.reply(wrapped); '
                     '}',
                   );
diff --git a/packages/pigeon/lib/objc_generator.dart b/packages/pigeon/lib/objc_generator.dart
index 54665b825a..caec03d65c 100644
--- a/packages/pigeon/lib/objc_generator.dart
+++ b/packages/pigeon/lib/objc_generator.dart
@@ -250,7 +250,7 @@ void _writeHostApiSource(Indent indent, ObjcOptions options, Api api) {
             }
             if (func.isAsynchronous) {
               if (func.returnType == 'void') {
-                const String callback = 'callback(error));';
+                const String callback = 'callback(error);';
                 if (func.argType == 'void') {
                   indent.writeScoped(
                       '[api ${func.name}:^(FlutterError *_Nullable error) {',
diff --git a/packages/pigeon/pigeons/async_handlers.dart b/packages/pigeon/pigeons/async_handlers.dart
index 67c439e7ae..6e2cb02a0c 100644
--- a/packages/pigeon/pigeons/async_handlers.dart
+++ b/packages/pigeon/pigeons/async_handlers.dart
@@ -12,6 +12,8 @@ class Value {
 abstract class Api2Host {
   @async
   Value calculate(Value value);
+  @async
+  void voidVoid();
 }
 
 @FlutterApi()