diff --git a/ext/opcache/jit/zend_jit.c b/ext/opcache/jit/zend_jit.c
index 9adfe1719f626..7caa3387016e7 100644
--- a/ext/opcache/jit/zend_jit.c
+++ b/ext/opcache/jit/zend_jit.c
@@ -4628,8 +4628,16 @@ ZEND_EXT_API int zend_jit_script(zend_script *script)
 	 || JIT_G(trigger) == ZEND_JIT_ON_HOT_TRACE) {
 		zend_class_entry *ce;
 		zend_op_array *op_array;
+		zval *zv;
+
+		ZEND_HASH_MAP_FOREACH_VAL(&script->class_table, zv) {
+			if (Z_TYPE_P(zv) == IS_ALIAS_PTR) {
+				continue;
+			}
+
+			ce = Z_PTR_P(zv);
+			ZEND_ASSERT(ce->type == ZEND_USER_CLASS);
 
-		ZEND_HASH_MAP_FOREACH_PTR(&script->class_table, ce) {
 			ZEND_HASH_MAP_FOREACH_PTR(&ce->function_table, op_array) {
 				if (!ZEND_FUNC_INFO(op_array)) {
 					void *jit_extension = zend_shared_alloc_get_xlat_entry(op_array->opcodes);
diff --git a/ext/opcache/tests/gh18639.phpt b/ext/opcache/tests/gh18639.phpt
new file mode 100644
index 0000000000000..28424032931ab
--- /dev/null
+++ b/ext/opcache/tests/gh18639.phpt
@@ -0,0 +1,20 @@
+--TEST--
+GH-18639 (Internal class aliases can break preloading + JIT)
+--INI--
+opcache.enable=1
+opcache.enable_cli=1
+opcache.jit=1255
+opcache.jit_buffer_size=16M
+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
+echo "ok\n";
+?>
+--EXPECT--
+ok