diff --git a/ext/spl/ArrayIteratorBuiltin.php b/ext/spl/ArrayIteratorBuiltin.php
index a51503a7a61..414e0ee4e30 100644
--- a/ext/spl/ArrayIteratorBuiltin.php
+++ b/ext/spl/ArrayIteratorBuiltin.php
@@ -257,9 +257,15 @@ public function execute(Frame $frame): void
             ArrayIteratorBuiltin::CLASS_LC,
             'ArrayIterator::seek()'
         );
-        // php-src zim_ArrayIterator_seek — exactly 1 user arg (#30963)
+        // php-src zim_ArrayIterator_seek — exactly 1 user arg (#30963); Z_PARAM_LONG soft-null (#31730).
         $this->requireExactUserArgCount($frame, 'ArrayIterator::seek', 1);
-        $offset = $frame->calledArgs[1]->resolveIndirect()->toInt();
+        $offset = VmMath::parseZParamLongBuiltinArgForFrame(
+            $frame,
+            1,
+            'ArrayIterator::seek',
+            1,
+            'offset'
+        );
         ArrayIteratorBuiltin::seek($object, $offset);
     }
 }
diff --git a/test/compliance/cases/stdlib/arrayiterator_seek_null_soft.phpt b/test/compliance/cases/stdlib/arrayiterator_seek_null_soft.phpt
new file mode 100644
index 00000000000..239fc8eff82
--- /dev/null
+++ b/test/compliance/cases/stdlib/arrayiterator_seek_null_soft.phpt
@@ -0,0 +1,24 @@
+--TEST--
+ArrayIterator::seek(null) — soft-null DEP then offset 0 (#31730)
+--FILE--
+<?php
+error_reporting(E_ALL);
+set_error_handler(static function (int $no, string $msg): bool {
+    if (E_DEPRECATED === $no) {
+        echo "DEP:{$msg}\n";
+        return true;
+    }
+    echo "E{$no}:{$msg}\n";
+    return true;
+});
+$ai = new ArrayIterator([10, 20, 30]);
+try {
+    $ai->seek(null);
+    echo 'key=' . $ai->key() . ' current=' . $ai->current() . "\n";
+} catch (Throwable $e) {
+    echo get_class($e) . ': ' . $e->getMessage() . "\n";
+}
+?>
+--EXPECT--
+DEP:ArrayIterator::seek(): Passing null to parameter #1 ($offset) of type int is deprecated
+key=0 current=10
diff --git a/test/unit/Issue31730ArrayIteratorSeekNullTest.php b/test/unit/Issue31730ArrayIteratorSeekNullTest.php
new file mode 100644
index 00000000000..ff435e530e1
--- /dev/null
+++ b/test/unit/Issue31730ArrayIteratorSeekNullTest.php
@@ -0,0 +1,118 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * ArrayIterator::seek(null) — soft-null E_DEPRECATED then seek 0 (#31730).
+ *
+ * php-src: ext/spl/spl_array.c — SPL_METHOD(Array, seek)
+ */
+final class Issue31730ArrayIteratorSeekNullTest extends TestCase
+{
+    public function testVmSeekNullDeprecationThenOffsetZero(): void
+    {
+        $out = $this->runBin('bin/vm.php', $this->softProbeCode());
+        $this->assertSame($this->expectedSoftOutput(), $out);
+    }
+
+    public function testJitSeekNullDeprecationThenOffsetZero(): void
+    {
+        $out = $this->runBin('bin/jit.php', $this->softProbeCode());
+        $this->assertSame($this->expectedSoftOutput(), $out);
+    }
+
+    public function testVmStrictTypesSeekNullTypeError(): void
+    {
+        $out = $this->runBin('bin/vm.php', $this->strictProbeCode());
+        $this->assertSame(
+            "TypeError: ArrayIterator::seek(): Argument #1 (\$offset) must be of type int, null given\n",
+            $out
+        );
+    }
+
+    public function testJitStrictTypesSeekNullTypeError(): void
+    {
+        $out = $this->runBin('bin/jit.php', $this->strictProbeCode());
+        $this->assertSame(
+            "TypeError: ArrayIterator::seek(): Argument #1 (\$offset) must be of type int, null given\n",
+            $out
+        );
+    }
+
+    private function expectedSoftOutput(): string
+    {
+        return "DEP:ArrayIterator::seek(): Passing null to parameter #1 (\$offset) of type int is deprecated\n"
+            ."key=0 current=10\n";
+    }
+
+    private function softProbeCode(): string
+    {
+        return <<<'PHP'
+<?php
+error_reporting(E_ALL);
+set_error_handler(static function (int $no, string $msg): bool {
+    if (E_DEPRECATED === $no) {
+        echo "DEP:{$msg}\n";
+        return true;
+    }
+    echo "E{$no}:{$msg}\n";
+    return true;
+});
+$ai = new ArrayIterator([10, 20, 30]);
+try {
+    $ai->seek(null);
+    echo 'key=' . $ai->key() . ' current=' . $ai->current() . "\n";
+} catch (Throwable $e) {
+    echo get_class($e) . ': ' . $e->getMessage() . "\n";
+}
+PHP;
+    }
+
+    private function strictProbeCode(): string
+    {
+        return <<<'PHP'
+<?php
+declare(strict_types=1);
+error_reporting(E_ALL);
+$ai = new ArrayIterator([10, 20, 30]);
+try {
+    $ai->seek(null);
+    echo "ok\n";
+} catch (Throwable $e) {
+    echo get_class($e), ': ', $e->getMessage(), "\n";
+}
+PHP;
+    }
+
+    private function runBin(string $bin, string $code): string
+    {
+        $repo = dirname(__DIR__, 2);
+        $tmp = tempnam(sys_get_temp_dir(), 'phpc_31730_');
+        $this->assertNotFalse($tmp);
+        file_put_contents($tmp, $code);
+        $env = $_ENV;
+        LlvmToolchain::applyProcessEnv($env, $repo);
+        $proc = proc_open(
+            ['php', $repo.'/'.$bin, $tmp],
+            [0 => ['pipe', 'r'], 1 => ['pipe', 'w'], 2 => ['pipe', 'w']],
+            $pipes,
+            $repo,
+            $env
+        );
+        $this->assertIsResource($proc);
+        fclose($pipes[0]);
+        $stdout = stream_get_contents($pipes[1]);
+        $stderr = stream_get_contents($pipes[2]);
+        fclose($pipes[1]);
+        fclose($pipes[2]);
+        $exit = proc_close($proc);
+        @unlink($tmp);
+        $this->assertSame(0, $exit, $stdout.$stderr);
+
+        return $stdout;
+    }
+}