diff --git a/src/Collection.php b/src/Collection.php
index ab82cca5d..f872f4aa2 100644
--- a/src/Collection.php
+++ b/src/Collection.php
@@ -77,7 +77,11 @@
 use function array_key_exists;
 use function current;
 use function is_array;
+use function sprintf;
 use function strlen;
+use function trigger_error;
+
+use const E_USER_DEPRECATED;
 
 class Collection
 {
@@ -952,6 +956,8 @@ public function listSearchIndexes(array $options = []): Iterator
      */
     public function mapReduce(JavascriptInterface $map, JavascriptInterface $reduce, string|array|object $out, array $options = [])
     {
+        @trigger_error(sprintf('The %s method is deprecated and will be removed in a future release.', __METHOD__), E_USER_DEPRECATED);
+
         $hasOutputCollection = ! is_mapreduce_output_inline($out);
 
         // Check if the out option is inline because we will want to coerce a primary read preference if not
diff --git a/tests/Collection/CollectionFunctionalTest.php b/tests/Collection/CollectionFunctionalTest.php
index d00ebd84e..d63140ca4 100644
--- a/tests/Collection/CollectionFunctionalTest.php
+++ b/tests/Collection/CollectionFunctionalTest.php
@@ -433,7 +433,9 @@ public function testMapReduce(): void
         $reduce = new Javascript('function(key, values) { return Array.sum(values); }');
         $out = ['inline' => 1];
 
-        $result = $this->collection->mapReduce($map, $reduce, $out);
+        $result = $this->assertDeprecated(
+            fn () => $this->collection->mapReduce($map, $reduce, $out),
+        );
 
         $this->assertInstanceOf(MapReduceResult::class, $result);
         $expected = [
diff --git a/tests/TestCase.php b/tests/TestCase.php
index 1d965606d..abc330ad8 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -160,7 +160,7 @@ final public static function provideInvalidStringValues(): array
         return self::wrapValuesForDataProvider(self::getInvalidStringValues());
     }
 
-    protected function assertDeprecated(callable $execution): void
+    protected function assertDeprecated(callable $execution)
     {
         $errors = [];
 
@@ -169,12 +169,14 @@ protected function assertDeprecated(callable $execution): void
         }, E_USER_DEPRECATED);
 
         try {
-            call_user_func($execution);
+            $result = call_user_func($execution);
         } finally {
             restore_error_handler();
         }
 
         $this->assertCount(1, $errors);
+
+        return $result;
     }
 
     protected static function createOptionDataProvider(array $options): array