diff --git a/lib/JIT/Builtin/Type/Object_.php b/lib/JIT/Builtin/Type/Object_.php
index e4465442509..a815779f872 100755
--- a/lib/JIT/Builtin/Type/Object_.php
+++ b/lib/JIT/Builtin/Type/Object_.php
@@ -1827,7 +1827,9 @@ public function registerClassAlias(string $original, string $alias): bool
 
         $classId = $this->classes[$originalLc];
         if (isset($this->externalOnlyClassIds[$classId])) {
-            return false;
+            throw new \ValueError(
+                'class_alias(): Argument #1 ($class) must be a user-defined class name, internal class name given'
+            );
         }
 
         $this->classes[$aliasLc] = $classId;
diff --git a/lib/VM/Context.php b/lib/VM/Context.php
index 4338e588ede..318153bc9bc 100755
--- a/lib/VM/Context.php
+++ b/lib/VM/Context.php
@@ -544,6 +544,11 @@ public function registerClassAlias(string $original, string $alias, bool $autolo
         }
 
         $entry = $this->classes[$originalLc];
+        if ($entry->isInternal) {
+            throw new \ValueError(
+                'class_alias(): Argument #1 ($class) must be a user-defined class name, internal class name given'
+            );
+        }
         $this->classes[$aliasLc] = $entry;
         $this->classAliases[$aliasLc] = $originalLc;
         if ($entry->isEnum) {
diff --git a/test/compliance/cases/stdlib/class_alias_internal.phpt b/test/compliance/cases/stdlib/class_alias_internal.phpt
new file mode 100644
index 00000000000..b1165ba8750
--- /dev/null
+++ b/test/compliance/cases/stdlib/class_alias_internal.phpt
@@ -0,0 +1,15 @@
+--TEST--
+stdlib class_alias() rejects internal class targets (#9211, Zend/zend_builtin_functions.c)
+--FILE--
+<?php
+try {
+    class_alias('stdClass', 'SC9211');
+    echo "alias ok\n";
+} catch (Throwable $e) {
+    echo get_class($e), ': ', $e->getMessage(), "\n";
+}
+var_export(class_exists('SC9211', false));
+echo "\n";
+--EXPECT--
+ValueError: class_alias(): Argument #1 ($class) must be a user-defined class name, internal class name given
+false
diff --git a/test/repro/maintainer_gap_class_alias_internal.php b/test/repro/maintainer_gap_class_alias_internal.php
new file mode 100644
index 00000000000..f8bb8750c23
--- /dev/null
+++ b/test/repro/maintainer_gap_class_alias_internal.php
@@ -0,0 +1,11 @@
+<?php
+declare(strict_types=1);
+
+try {
+    class_alias('stdClass', 'SC2');
+    echo "alias ok\n";
+} catch (Throwable $e) {
+    echo get_class($e), ': ', $e->getMessage(), "\n";
+}
+var_export(class_exists('SC2', false));
+echo "\n";