diff --git a/ext/standard/JitStreamFilter.php b/ext/standard/JitStreamFilter.php
index 4ba1e0b2c19..3842f5d9da7 100644
--- a/ext/standard/JitStreamFilter.php
+++ b/ext/standard/JitStreamFilter.php
@@ -157,7 +157,23 @@ private static function attach(Context $context, string $abi, string $functionNa
             JitLongArg::lower($context, $args[0], $functionName.'() stream'),
             $context->getTypeFromString('int64')
         );
-        $filterName = JitStringBuiltinArg::lower($context, $args[1], $functionName, 1, 'filtername');
+        // Z_PARAM_STR $filter_name — TypeError under declare(strict_types=1) (#31408).
+        $filterName = JitStringBuiltinArg::lowerStrictOrCoercible(
+            $context,
+            $args[1],
+            $functionName,
+            1,
+            'filter_name'
+        );
+        // Catchable TypeError seals the insert block; open a dead BB so later attach
+        // IR does not land after a terminator (#31408 / peer #30250 JitDl).
+        if ($context->callerStrictTypes
+            && (JITVariable::TYPE_NULL === $args[1]->type || ($args[1]->isNullConstant ?? false))
+        ) {
+            BasicBlockHelper::ensureOpenInsertBlock($context, $functionName.'_strict_null_dead');
+
+            return self::boolBox($context, $context->getTypeFromString('int1')->constInt(0, false));
+        }
         $i64 = $context->getTypeFromString('int64');
         $readWrite = $i64->constInt(VmStreamFilterChain::ALL, false);
         if ($argc >= 3) {
diff --git a/ext/standard/stream_filter_append.php b/ext/standard/stream_filter_append.php
index b08b4b4457d..40b0e4c94a7 100644
--- a/ext/standard/stream_filter_append.php
+++ b/ext/standard/stream_filter_append.php
@@ -8,6 +8,7 @@
 use PHPCompiler\Func\Internal;
 use PHPCompiler\JIT\Context;
 use PHPCompiler\JIT\Variable as JITVariable;
+use PHPCompiler\VM\InternalStrictArg;
 use PHPLLVM\Value;
 
 /** stream_filter_append() — attach a filter to a stream (#3283, ext/standard/streams.c). */
@@ -31,10 +32,11 @@ public function execute(Frame $frame): void
             'stream_filter_append',
             1
         );
-        $filterName = VmString::coerceStringBuiltinArg(
-            $frame->calledArgs[1],
-            'stream_filter_append',
+        // Z_PARAM_STR $filter_name — TypeError under declare(strict_types=1) (#31408).
+        $filterName = InternalStrictArg::resolveCoercibleStringArg(
+            $frame,
             1,
+            'stream_filter_append',
             'filter_name'
         );
         $readWrite = VmStreamFilterChain::ALL;
diff --git a/ext/standard/stream_filter_prepend.php b/ext/standard/stream_filter_prepend.php
index fcf5fb9573f..c339a9f51b4 100644
--- a/ext/standard/stream_filter_prepend.php
+++ b/ext/standard/stream_filter_prepend.php
@@ -8,6 +8,7 @@
 use PHPCompiler\Func\Internal;
 use PHPCompiler\JIT\Context;
 use PHPCompiler\JIT\Variable as JITVariable;
+use PHPCompiler\VM\InternalStrictArg;
 use PHPLLVM\Value;
 
 /** stream_filter_prepend() — attach a filter at the head of a stream chain (#3283). */
@@ -31,10 +32,11 @@ public function execute(Frame $frame): void
             'stream_filter_prepend',
             1
         );
-        $filterName = VmString::coerceStringBuiltinArg(
-            $frame->calledArgs[1],
-            'stream_filter_prepend',
+        // Z_PARAM_STR $filter_name — TypeError under declare(strict_types=1) (#31408).
+        $filterName = InternalStrictArg::resolveCoercibleStringArg(
+            $frame,
             1,
+            'stream_filter_prepend',
             'filter_name'
         );
         $readWrite = VmStreamFilterChain::ALL;
diff --git a/test/repro/maintainer_gap_stream_filter_append_null_name.php b/test/repro/maintainer_gap_stream_filter_append_null_name.php
index 4f0835c6711..658be216fae 100644
--- a/test/repro/maintainer_gap_stream_filter_append_null_name.php
+++ b/test/repro/maintainer_gap_stream_filter_append_null_name.php
@@ -1,9 +1,18 @@
 <?php
 declare(strict_types=1);
-// Maintainer gap probe: stream_filter_append($stream, null) under strict_types.
+// Maintainer gap probe: stream_filter_append/prepend($stream, null) under strict_types (#31408).
 // Zend: TypeError Argument #2 ($filter_name) must be of type string, null given
-// VM (2026-08-16): coerces null→"" then warns unable to locate filter ""
 $h = fopen('php://memory', 'r+');
-var_export(stream_filter_append($h, null));
-echo "\n";
+try {
+    stream_filter_append($h, null);
+    echo "NO_THROW_APPEND\n";
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+try {
+    stream_filter_prepend($h, null);
+    echo "NO_THROW_PREPEND\n";
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
 fclose($h);
diff --git a/test/unit/Issue31408StreamFilterNullNameStrictAotTest.php b/test/unit/Issue31408StreamFilterNullNameStrictAotTest.php
new file mode 100644
index 00000000000..ccc5ef5e226
--- /dev/null
+++ b/test/unit/Issue31408StreamFilterNullNameStrictAotTest.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * AOT: stream_filter_append/prepend null $filter_name under strict_types → TypeError (#31408).
+ *
+ * php-src: ext/standard/streamsfuncs.c / basic_functions.stub.php — string $filter_name
+ *
+ * @group llvm
+ * @group aot
+ */
+final class Issue31408StreamFilterNullNameStrictAotTest extends TestCase
+{
+    public function testAotNullFilterNameStrictTypeError(): void
+    {
+        if (!LlvmToolchain::hasLibrary(dirname(__DIR__, 2))) {
+            $this->markTestSkipped('LLVM 9 toolchain not available');
+        }
+        $root = dirname(__DIR__, 2);
+        $src = sys_get_temp_dir().'/phpc_31408_'.getmypid().'.php';
+        $bin = sys_get_temp_dir().'/phpc_31408_'.getmypid().'.bin';
+        file_put_contents($src, <<<'PHP'
+<?php
+declare(strict_types=1);
+$h = fopen('php://memory', 'r+');
+try {
+    stream_filter_append($h, null);
+    echo "NO_THROW_APPEND\n";
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+try {
+    stream_filter_prepend($h, null);
+    echo "NO_THROW_PREPEND\n";
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+fclose($h);
+PHP);
+        $compile = escapeshellarg(PHP_BINARY).' '
+            .escapeshellarg($root.'/bin/compile.php')
+            .' -o '.escapeshellarg($bin).' '.escapeshellarg($src).' 2>&1';
+        exec($compile, $compileOut, $compileRc);
+        $this->assertSame(0, $compileRc, implode("\n", $compileOut));
+        $this->assertFileExists($bin);
+        try {
+            for ($i = 0; $i < 3; ++$i) {
+                $runOut = [];
+                exec(escapeshellarg($bin).' 2>&1', $runOut, $runRc);
+                $this->assertSame(0, $runRc, 'run '.($i + 1).': '.implode("\n", $runOut));
+                $joined = implode("\n", $runOut)."\n";
+                $this->assertSame(
+                    "TypeError: stream_filter_append(): Argument #2 (\$filter_name) must be of type string, null given\n"
+                    ."TypeError: stream_filter_prepend(): Argument #2 (\$filter_name) must be of type string, null given\n",
+                    $joined
+                );
+                $this->assertStringNotContainsString('unable to locate filter', $joined);
+            }
+        } finally {
+            @unlink($src);
+            @unlink($bin);
+        }
+    }
+}
diff --git a/test/unit/Issue31408StreamFilterNullNameStrictTest.php b/test/unit/Issue31408StreamFilterNullNameStrictTest.php
new file mode 100644
index 00000000000..5e21193b899
--- /dev/null
+++ b/test/unit/Issue31408StreamFilterNullNameStrictTest.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * stream_filter_append/prepend null $filter_name under strict_types → TypeError (#31408).
+ *
+ * php-src: ext/standard/streamsfuncs.c / basic_functions.stub.php — string $filter_name
+ */
+final class Issue31408StreamFilterNullNameStrictTest extends TestCase
+{
+    public function testVmNullFilterNameStrictTypeError(): void
+    {
+        $code = file_get_contents(__DIR__.'/../repro/maintainer_gap_stream_filter_append_null_name.php');
+        $this->assertNotFalse($code);
+        $rt = new Runtime();
+        $block = $rt->parseAndCompile($code, 'maintainer_gap_stream_filter_append_null_name.php');
+        ob_start();
+        $rt->run($block);
+        $out = ob_get_clean();
+        $this->assertSame(
+            "TypeError: stream_filter_append(): Argument #2 (\$filter_name) must be of type string, null given\n"
+            ."TypeError: stream_filter_prepend(): Argument #2 (\$filter_name) must be of type string, null given\n",
+            $out
+        );
+        $this->assertStringNotContainsString('unable to locate filter', $out);
+        $this->assertStringNotContainsString('NO_THROW', $out);
+    }
+}