diff --git a/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/replace_return_type.php.inc b/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/replace_return_type.php.inc
new file mode 100644
index 00000000..0a5c6a18
--- /dev/null
+++ b/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/replace_return_type.php.inc
@@ -0,0 +1,40 @@
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\MergeWithCallableAndWillReturnRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+final class ReplaceReturnType extends TestCase
+{
+    public function test()
+    {
+        $this->createMock('SomeClass')
+            ->method('someMethod')
+            ->with($this->callback(function ($arg): bool {
+                return true;
+            }))
+            ->willReturn('someValue');
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\PHPUnit\Tests\CodeQuality\Rector\MethodCall\MergeWithCallableAndWillReturnRector\Fixture;
+
+use PHPUnit\Framework\TestCase;
+
+final class ReplaceReturnType extends TestCase
+{
+    public function test()
+    {
+        $this->createMock('SomeClass')
+            ->method('someMethod')
+            ->willReturnCallback(function ($arg): string {
+                return 'someValue';
+            });
+    }
+}
+
+?>
diff --git a/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/with_callback_and_will_return.php.inc b/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/with_callback_and_will_return.php.inc
index d62d7525..b9446c73 100644
--- a/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/with_callback_and_will_return.php.inc
+++ b/rules-tests/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector/Fixture/with_callback_and_will_return.php.inc
@@ -31,7 +31,7 @@ final class WithCallbackAndWillReturn extends TestCase
     {
         $this->createMock('SomeClass')
             ->method('someMethod')
-            ->willReturnCallback(function ($arg) {
+            ->willReturnCallback(function ($arg): string {
                 return 'someValue';
             });
     }
diff --git a/rules/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector.php b/rules/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector.php
index bc3147b1..ea0577a5 100644
--- a/rules/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector.php
+++ b/rules/CodeQuality/Rector/MethodCall/MergeWithCallableAndWillReturnRector.php
@@ -11,8 +11,10 @@
 use PhpParser\Node\Identifier;
 use PhpParser\Node\Stmt\Return_;
 use Rector\PhpParser\Node\Value\ValueResolver;
+use Rector\PHPStanStaticTypeMapper\Enum\TypeKind;
 use Rector\PHPUnit\NodeAnalyzer\TestsNodeAnalyzer;
 use Rector\Rector\AbstractRector;
+use Rector\StaticTypeMapper\StaticTypeMapper;
 use Symplify\RuleDocGenerator\ValueObject\CodeSample\CodeSample;
 use Symplify\RuleDocGenerator\ValueObject\RuleDefinition;
 
@@ -24,6 +26,7 @@ final class MergeWithCallableAndWillReturnRector extends AbstractRector
     public function __construct(
         private readonly TestsNodeAnalyzer $testsNodeAnalyzer,
         private readonly ValueResolver $valueResolver,
+        private readonly StaticTypeMapper $staticTypeMapper,
     ) {
     }
 
@@ -131,12 +134,17 @@ public function refactor(Node $node): MethodCall|null
 
         /** @var Return_ $return */
         $return = $innerClosure->stmts[count($innerClosure->stmts) - 1];
-        $return->expr = $willReturnMethodCall->getArgs()[0]
+        $returnedExpr = $willReturnMethodCall->getArgs()[0]
             ->value;
+        $return->expr = $returnedExpr;
 
         $parentCaller->name = new Identifier('willReturnCallback');
         $parentCaller->args = [new Arg($innerClosure)];
 
+        $returnedExprType = $this->staticTypeMapper->mapPhpParserNodePHPStanType($returnedExpr);
+        $returnTypeNode = $this->staticTypeMapper->mapPHPStanTypeToPhpParserNode($returnedExprType, TypeKind::RETURN);
+        $innerClosure->returnType = $returnTypeNode instanceof Node ? $returnTypeNode : null;
+
         return $parentCaller;
     }