diff --git a/src/Client.php b/src/Client.php
index 4ffc265..9dcaacc 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -1726,6 +1726,49 @@ public function toArray(mixed $obj): ?array
         return $ret;
     }
 
+    /**
+     * Replace BSON Int64 wrappers with native PHP integers.
+     *
+     * MongoDB\BSON\Document::toPHP() decodes every 64-bit BSON integer as an
+     * Int64 object on all platforms, so any value outside the int32 range comes
+     * back wrapped. Callers expect plain PHP values, and an Int64 that survives
+     * into user code either fatals when array-accessed or degrades to 1 under an
+     * (int) cast. On 64-bit PHP the unwrap is lossless; on 32-bit builds the
+     * wrapper is the only representation that preserves precision, so it stays.
+     *
+     * @param mixed $value
+     * @param array<string, true> $skip Top-level keys to leave untouched
+     * @return mixed
+     */
+    private static function normalizeInt64(mixed $value, array $skip = []): mixed
+    {
+        if ($value instanceof Int64) {
+            return \PHP_INT_SIZE >= 8 ? (int)(string)$value : $value;
+        }
+
+        if (\is_array($value)) {
+            foreach ($value as $key => $item) {
+                $value[$key] = self::normalizeInt64($item);
+            }
+
+            return $value;
+        }
+
+        if ($value instanceof stdClass) {
+            foreach (\get_object_vars($value) as $key => $item) {
+                if (isset($skip[$key])) {
+                    continue;
+                }
+
+                $value->{$key} = self::normalizeInt64($item);
+            }
+
+            return $value;
+        }
+
+        return $value;
+    }
+
     private function cleanFilters($filters): array
     {
         $cleanedFilters = [];
@@ -1910,6 +1953,11 @@ private function parseResponse(string $response, int $responseLength): stdClass|
             if (\is_array($result)) {
                 $result = (object)$result;
             }
+
+            // $clusterTime is echoed back to the server verbatim on subsequent
+            // commands, so its BSON types must survive intact — signature.keyId
+            // is an int64 the server rejects if it comes back as an int32.
+            $result = self::normalizeInt64($result, ['$clusterTime' => true]);
         } catch (\Throwable $error) {
             $this->invalidate();
             throw new Exception('Failed to parse BSON response: ' . $error->getMessage(), 0, $error);
diff --git a/tests/MongoTest.php b/tests/MongoTest.php
index f69f481..34754e2 100644
--- a/tests/MongoTest.php
+++ b/tests/MongoTest.php
@@ -320,6 +320,60 @@ public function testToArrayWithNestedDocumentFromMongo()
         $client->dropCollection('movies_nested');
     }
 
+    public function testInt64ValuesDecodeToNativeIntegers()
+    {
+        if (\PHP_INT_SIZE < 8) {
+            // normalizeInt64() deliberately keeps the wrapper on 32-bit builds,
+            // where it is the only lossless representation, and the literals
+            // below would already be floats before reaching the driver.
+            self::markTestSkipped('Native int64 round-trip requires a 64-bit PHP build.');
+        }
+
+        $client = $this->getDatabase();
+
+        // Beyond the int32 range, so MongoDB stores these as BSON int64 and
+        // Document::toPHP() hands them back as MongoDB\BSON\Int64 wrappers.
+        $negative = -3408048000;
+        $positive = 3408048000;
+        $extreme = \PHP_INT_MAX;
+
+        try {
+            $client->insert('movies_int64', [
+                '_id' => 'int64-test-1',
+                'small' => -42,
+                'big' => $negative,
+                'list' => [$negative, -42, $positive, $extreme],
+                'nested' => ['deep' => ['value' => $negative]],
+            ]);
+
+            $result = $client->find('movies_int64', ['_id' => 'int64-test-1'])->cursor->firstBatch[0] ?? null;
+            self::assertNotNull($result);
+
+            self::assertIsInt($result->small);
+            self::assertSame(-42, $result->small);
+
+            self::assertIsInt($result->big);
+            self::assertSame($negative, $result->big);
+
+            self::assertIsInt($result->list[0]);
+            self::assertSame($negative, $result->list[0]);
+            self::assertSame(-42, $result->list[1]);
+            self::assertSame($positive, $result->list[2]);
+            self::assertSame($extreme, $result->list[3]);
+
+            self::assertIsInt($result->nested->deep->value);
+            self::assertSame($negative, $result->nested->deep->value);
+
+            // toArray() must carry the native integers through untouched.
+            $array = $client->toArray($result);
+            self::assertSame($negative, $array['big']);
+            self::assertSame([$negative, -42, $positive, $extreme], $array['list']);
+            self::assertSame($negative, $array['nested']['deep']['value']);
+        } finally {
+            $client->dropCollection('movies_int64');
+        }
+    }
+
     public function testToArrayNestedConversion()
     {
         $client = $this->getDatabase();