diff --git a/lib/JIT/Builtin/StringNaturalCompareJit.php b/lib/JIT/Builtin/StringNaturalCompareJit.php
index 8e8ca1ffa9b..f4425e307ca 100644
--- a/lib/JIT/Builtin/StringNaturalCompareJit.php
+++ b/lib/JIT/Builtin/StringNaturalCompareJit.php
@@ -5,7 +5,6 @@
 namespace PHPCompiler\JIT\Builtin;
 
 use PHPCompiler\JIT\BasicBlockHelper;
-use PHPCompiler\JIT\Builtin;
 use PHPCompiler\JIT\Context;
 use PHPLLVM\BasicBlock;
 use PHPLLVM\Builder;
@@ -13,7 +12,9 @@
 use PHPLLVM\Value\Function_ as LlvmFunction;
 
 /**
- * LLVM natural-order string compare (mirrors VmString::strnatcmp / strnatcasecmp, phpc_strnatcmp.c).
+ * LLVM natural-order string compare (mirrors VmString::strnatcmp / strnatcasecmp).
+ *
+ * Replaces deleted lib/AOT/runtime/phpc_strnatcmp.c + phpc_strnatcasecmp.c (#5517).
  */
 final class StringNaturalCompareJit
 {
@@ -29,12 +30,6 @@ public static function implementStrnatcasecmp(Context $context): void
 
     private static function implementNamed(Context $context, string $name, bool $caseInsensitive): void
     {
-        if (Builtin::LOAD_TYPE_STANDALONE === $context->loadType) {
-            self::declareIfMissing($context, $name);
-
-            return;
-        }
-
         $probe = $context->module->getNamedFunction($name);
         if (null !== $probe && $probe->countBasicBlocks() > 0) {
             $context->registerFunction($name, $probe);
diff --git a/test/compliance/StrnatcmpJITTest.php b/test/compliance/StrnatcmpJITTest.php
new file mode 100644
index 00000000000..c50f8cf2390
--- /dev/null
+++ b/test/compliance/StrnatcmpJITTest.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+require_once __DIR__.'/../BaseTest.php';
+
+/**
+ * @group llvm
+ */
+/** JIT compliance for strnatcmp() / strnatcasecmp(). */
+final class StrnatcmpJITTest extends BaseTest
+{
+    protected static string $DIR = __DIR__;
+
+    public static function providePHPTests(): \Generator
+    {
+        yield 'strnatcmp_jit.phpt' => self::parsePHPT(
+            __DIR__.'/cases/stdlib/strnatcmp_jit.phpt',
+            'strnatcmp_jit.phpt'
+        );
+    }
+
+    public function setUp(): void
+    {
+        $this->BIN = realpath(__DIR__.'/../../bin/jit.php');
+    }
+}
diff --git a/test/compliance/cases/stdlib/strnatcmp_jit.phpt b/test/compliance/cases/stdlib/strnatcmp_jit.phpt
new file mode 100644
index 00000000000..10cceb8335c
--- /dev/null
+++ b/test/compliance/cases/stdlib/strnatcmp_jit.phpt
@@ -0,0 +1,14 @@
+--TEST--
+JIT: strnatcmp() / strnatcasecmp() (#5517)
+--FILE--
+<?php
+var_export(strnatcmp('2', '10'));
+echo "\n";
+var_export(strnatcmp('10', '2'));
+echo "\n";
+var_export(strnatcasecmp('aB', 'Ab'));
+echo "\n";
+--EXPECT--
+-1
+1
+0
diff --git a/test/fixtures/aot/cases/strnatcmp.phpt b/test/fixtures/aot/cases/strnatcmp.phpt
new file mode 100644
index 00000000000..55bf13bf30a
--- /dev/null
+++ b/test/fixtures/aot/cases/strnatcmp.phpt
@@ -0,0 +1,11 @@
+--TEST--
+AOT: strnatcmp() / strnatcasecmp() (#5517)
+--FILE--
+<?php
+var_export(strnatcmp('2', '10'));
+echo "\n";
+var_export(strnatcasecmp('aB', 'Ab'));
+echo "\n";
+--EXPECT--
+-1
+0
diff --git a/test/unit/JIT/StringNaturalCompareStandaloneTest.php b/test/unit/JIT/StringNaturalCompareStandaloneTest.php
new file mode 100644
index 00000000000..f038c6a88d3
--- /dev/null
+++ b/test/unit/JIT/StringNaturalCompareStandaloneTest.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler\JIT;
+
+use PHPCompiler\JIT\Builtin\StringNaturalCompareJit;
+use PHPCompiler\Runtime;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Issue #5517: AOT standalone must define strnatcmp/strnatcasecmp without phpc_strnatcmp*.c.
+ *
+ * @group aot-lint
+ */
+final class StringNaturalCompareStandaloneTest extends TestCase
+{
+    public function testImplementDefinesNaturalCompareForStandalone(): void
+    {
+        $runtime = new Runtime(Runtime::MODE_AOT);
+        $ctx = new Context($runtime, Builtin::LOAD_TYPE_STANDALONE);
+        StringNaturalCompareJit::implementStrnatcmp($ctx);
+        StringNaturalCompareJit::implementStrnatcasecmp($ctx);
+
+        foreach (['strnatcmp', 'strnatcasecmp'] as $name) {
+            $fn = $ctx->lookupFunction($name);
+            $this->assertNotNull($fn);
+            $this->assertGreaterThan(0, $fn->countBasicBlocks());
+        }
+    }
+}