diff --git a/src/DbPager.php b/src/DbPager.php
index 34f7d20..2ccd6d0 100644
--- a/src/DbPager.php
+++ b/src/DbPager.php
@@ -23,6 +23,8 @@ public function __construct(
     /** @param array<string, mixed> $values */
     public function __invoke(string $queryId, array $values, Pager $pager, string|null $entity): PagesInterface
     {
+        // Clone the Pager attribute to avoid mutating the caller's instance in dynamicPager().
+        $pager = clone $pager;
         if (is_string($pager->perPage)) {
             $values = $this->dynamicPager($pager, $values);
         }
diff --git a/tests/DbPagerTest.php b/tests/DbPagerTest.php
new file mode 100644
index 0000000..89aa50e
--- /dev/null
+++ b/tests/DbPagerTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ray\MediaQuery;
+
+use PHPUnit\Framework\TestCase;
+use Ray\MediaQuery\Annotation\Pager;
+
+final class DbPagerTest extends TestCase
+{
+    public function testPagerInstanceIsNotMutatedAcrossCalls(): void
+    {
+        $sqlQuery = new FakeSqlQuery();
+        $dbPager = new DbPager(new FakeMediaQueryLogger(), $sqlQuery);
+
+        // The Pager attribute instance is shared across multiple calls,
+        // mirroring how a cached annotation would be reused in production code.
+        $pager = new Pager(perPage: 'perPage', template: '/{?page}');
+
+        foreach ([2, 1, 3] as $perPage) {
+            ($dbPager)('todo_list', ['perPage' => $perPage], $pager, null);
+        }
+
+        $this->assertSame('perPage', $pager->perPage, 'Pager::$perPage must remain the original key string');
+        $this->assertSame([2, 1, 3], $sqlQuery->perPageHistory, 'Each call must forward its own perPage to SqlQuery::getPages()');
+    }
+}
diff --git a/tests/Fake/FakeEmptyPages.php b/tests/Fake/FakeEmptyPages.php
new file mode 100644
index 0000000..c814381
--- /dev/null
+++ b/tests/Fake/FakeEmptyPages.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ray\MediaQuery;
+
+use ArrayIterator;
+
+final class FakeEmptyPages implements PagesInterface
+{
+    /** @var ArrayIterator<int, mixed> */
+    private ArrayIterator $iter;
+
+    public function __construct()
+    {
+        $this->iter = new ArrayIterator([]);
+    }
+
+    public function offsetExists(mixed $offset): bool
+    {
+        return $this->iter->offsetExists($offset);
+    }
+
+    public function offsetGet(mixed $offset): mixed
+    {
+        return $this->iter->offsetGet($offset);
+    }
+
+    public function offsetSet(mixed $offset, mixed $value): void
+    {
+        $this->iter->offsetSet($offset, $value);
+    }
+
+    public function offsetUnset(mixed $offset): void
+    {
+        $this->iter->offsetUnset($offset);
+    }
+
+    public function count(): int
+    {
+        return $this->iter->count();
+    }
+}
diff --git a/tests/Fake/FakeMediaQueryLogger.php b/tests/Fake/FakeMediaQueryLogger.php
new file mode 100644
index 0000000..9f16935
--- /dev/null
+++ b/tests/Fake/FakeMediaQueryLogger.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ray\MediaQuery;
+
+final class FakeMediaQueryLogger implements MediaQueryLoggerInterface
+{
+    public function start(): void
+    {
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function log(string $queryId, array $values): void
+    {
+    }
+
+    public function __toString(): string
+    {
+        return '';
+    }
+}
diff --git a/tests/Fake/FakeSqlQuery.php b/tests/Fake/FakeSqlQuery.php
new file mode 100644
index 0000000..1c54fc0
--- /dev/null
+++ b/tests/Fake/FakeSqlQuery.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ray\MediaQuery;
+
+final class FakeSqlQuery implements SqlQueryInterface
+{
+    /** @var list<int> */
+    public array $perPageHistory = [];
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function getRow(string $sqlId, array $values = [], FetchInterface|null $fetch = null): array|object|null
+    {
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function getRowList(string $sqlId, array $values = [], FetchInterface|null $fetch = null): array
+    {
+        return [];
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function exec(string $sqlId, array $values = [], FetchInterface|null $fetch = null): void
+    {
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function getCount(string $sqlId, array $values): int
+    {
+        return 0;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @param array<string, mixed> $values
+     */
+    public function getPages(string $sqlId, array $values, int $perPage, string $queryTemplate = '/{?page}', string|null $entity = null): PagesInterface
+    {
+        $this->perPageHistory[] = $perPage;
+
+        return new FakeEmptyPages();
+    }
+}