diff --git a/ext/opcache/ZendAccelerator.c b/ext/opcache/ZendAccelerator.c
index e3f7ca18151e5..47e0bc08bd5cc 100644
--- a/ext/opcache/ZendAccelerator.c
+++ b/ext/opcache/ZendAccelerator.c
@@ -3522,7 +3522,7 @@ static void preload_shutdown(void)
 	if (EG(class_table)) {
 		ZEND_HASH_MAP_REVERSE_FOREACH_VAL(EG(class_table), zv) {
 			zend_class_entry *ce = Z_PTR_P(zv);
-			if (ce->type == ZEND_INTERNAL_CLASS) {
+			if (ce->type == ZEND_INTERNAL_CLASS && Z_TYPE_P(zv) != IS_ALIAS_PTR) {
 				break;
 			}
 		} ZEND_HASH_MAP_FOREACH_END_DEL();
@@ -3610,7 +3610,15 @@ static void preload_move_user_classes(HashTable *src, HashTable *dst)
 	zend_hash_extend(dst, dst->nNumUsed + src->nNumUsed, 0);
 	ZEND_HASH_MAP_FOREACH_BUCKET_FROM(src, p, EG(persistent_classes_count)) {
 		zend_class_entry *ce = Z_PTR(p->val);
-		ZEND_ASSERT(ce->type == ZEND_USER_CLASS);
+
+		/* Possible with internal class aliases */
+		if (ce->type == ZEND_INTERNAL_CLASS) {
+			ZEND_ASSERT(Z_TYPE(p->val) == IS_ALIAS_PTR);
+			_zend_hash_append(dst, p->key, &p->val);
+			zend_hash_del_bucket(src, p);
+			continue;
+		}
+
 		if (ce->info.user.filename != filename) {
 			filename = ce->info.user.filename;
 			if (filename) {
@@ -3904,7 +3912,12 @@ static void preload_link(void)
 
 		ZEND_HASH_MAP_FOREACH_STR_KEY_VAL_FROM(EG(class_table), key, zv, EG(persistent_classes_count)) {
 			ce = Z_PTR_P(zv);
-			ZEND_ASSERT(ce->type != ZEND_INTERNAL_CLASS);
+
+			/* Possible with internal class aliases */
+			if (ce->type == ZEND_INTERNAL_CLASS) {
+				ZEND_ASSERT(Z_TYPE_P(zv) == IS_ALIAS_PTR);
+				continue;
+			}
 
 			if (!(ce->ce_flags & (ZEND_ACC_TOP_LEVEL|ZEND_ACC_ANON_CLASS))
 					|| (ce->ce_flags & ZEND_ACC_LINKED)) {
@@ -3990,9 +4003,15 @@ static void preload_link(void)
 
 		ZEND_HASH_MAP_REVERSE_FOREACH_VAL(EG(class_table), zv) {
 			ce = Z_PTR_P(zv);
+
+			/* Possible with internal class aliases */
 			if (ce->type == ZEND_INTERNAL_CLASS) {
-				break;
+				if (Z_TYPE_P(zv) != IS_ALIAS_PTR) {
+					break; /* can stop already */
+				}
+				continue;
 			}
+
 			if ((ce->ce_flags & ZEND_ACC_LINKED) && !(ce->ce_flags & ZEND_ACC_CONSTANTS_UPDATED)) {
 				if (!(ce->ce_flags & ZEND_ACC_TRAIT)) { /* don't update traits */
 					CG(in_compilation) = true; /* prevent autoloading */
@@ -4009,7 +4028,13 @@ static void preload_link(void)
 	ZEND_HASH_MAP_FOREACH_STR_KEY_VAL_FROM(
 			EG(class_table), key, zv, EG(persistent_classes_count)) {
 		ce = Z_PTR_P(zv);
-		ZEND_ASSERT(ce->type != ZEND_INTERNAL_CLASS);
+
+		/* Possible with internal class aliases */
+		if (ce->type == ZEND_INTERNAL_CLASS) {
+			ZEND_ASSERT(Z_TYPE_P(zv) == IS_ALIAS_PTR);
+			continue;
+		}
+
 		if ((ce->ce_flags & (ZEND_ACC_TOP_LEVEL|ZEND_ACC_ANON_CLASS))
 				&& !(ce->ce_flags & ZEND_ACC_LINKED)) {
 			zend_string *lcname = zend_string_tolower(ce->name);
diff --git a/ext/opcache/tests/gh18567.phpt b/ext/opcache/tests/gh18567.phpt
new file mode 100644
index 0000000000000..e1d2a68af6775
--- /dev/null
+++ b/ext/opcache/tests/gh18567.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-18567 (Preloading with internal class alias triggers assertion failure)
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.preload={PWD}/preload_gh18567.inc
+--EXTENSIONS--
+opcache
+--SKIPIF--
+<?php
+if (PHP_OS_FAMILY == 'Windows') die('skip Preloading is not supported on Windows');
+?>
+--FILE--
+<?php
+abstract class Test implements MyStringable {
+}
+$rc = new ReflectionClass(Test::class);
+var_dump($rc->getInterfaces());
+?>
+--EXPECT--
+array(1) {
+  ["Stringable"]=>
+  object(ReflectionClass)#2 (1) {
+    ["name"]=>
+    string(10) "Stringable"
+  }
+}
diff --git a/ext/opcache/tests/preload_gh18567.inc b/ext/opcache/tests/preload_gh18567.inc
new file mode 100644
index 0000000000000..d277e83f83be6
--- /dev/null
+++ b/ext/opcache/tests/preload_gh18567.inc
@@ -0,0 +1,2 @@
+<?php
+class_alias('Stringable', 'MyStringable');