diff --git a/Zend/tests/traits/gh12854.phpt b/Zend/tests/traits/gh12854.phpt
new file mode 100644
index 0000000000000..471b4c6b56558
--- /dev/null
+++ b/Zend/tests/traits/gh12854.phpt
@@ -0,0 +1,74 @@
+--TEST--
+GH-12854 (8.3 - as final trait-used method does not correctly report visibility in Reflection)
+--FILE--
+<?php
+
+trait SimpleTrait
+{
+    public function pub() {}
+    protected function prot() {}
+    private function priv() {}
+
+    public final function final1() {}
+    public final function final2() {}
+    public final function final3() {}
+}
+
+
+class Test
+{
+    use SimpleTrait {
+        pub as final;
+        prot as final;
+        priv as final;
+
+        final1 as private;
+        final2 as protected;
+        final3 as public;
+    }
+}
+
+foreach (['pub', 'prot', 'priv', 'final1', 'final2', 'final3'] as $method) {
+    echo "--- Method: $method ---\n";
+    $rm = new ReflectionMethod(Test::class, $method);
+    var_dump($rm->isFinal());
+    var_dump($rm->isPublic());
+    var_dump($rm->isProtected());
+    var_dump($rm->isPrivate());
+}
+
+?>
+--EXPECTF--
+Warning: Private methods cannot be final as they are never overridden by other classes in %s on line %d
+
+Warning: Private methods cannot be final as they are never overridden by other classes in %s on line %d
+--- Method: pub ---
+bool(true)
+bool(true)
+bool(false)
+bool(false)
+--- Method: prot ---
+bool(true)
+bool(false)
+bool(true)
+bool(false)
+--- Method: priv ---
+bool(true)
+bool(false)
+bool(false)
+bool(true)
+--- Method: final1 ---
+bool(true)
+bool(false)
+bool(false)
+bool(true)
+--- Method: final2 ---
+bool(true)
+bool(false)
+bool(true)
+bool(false)
+--- Method: final3 ---
+bool(true)
+bool(true)
+bool(false)
+bool(false)
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index d1c66b310a6b4..6362090ada908 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -1949,6 +1949,10 @@ static void zend_add_trait_method(zend_class_entry *ce, zend_string *name, zend_
 	zend_function *new_fn;
 	bool check_inheritance = false;
 
+	if ((fn->common.fn_flags & (ZEND_ACC_PRIVATE | ZEND_ACC_FINAL)) == (ZEND_ACC_PRIVATE | ZEND_ACC_FINAL)) {
+		zend_error(E_COMPILE_WARNING, "Private methods cannot be final as they are never overridden by other classes");
+	}
+
 	if ((existing_fn = zend_hash_find_ptr(&ce->function_table, key)) != NULL) {
 		/* if it is the same function with the same visibility and has not been assigned a class scope yet, regardless
 		 * of where it is coming from there is no conflict and we do not need to add it again */
@@ -2048,10 +2052,10 @@ static void zend_traits_copy_functions(zend_string *fnname, zend_function *fn, z
 				&& zend_string_equals_ci(alias->trait_method.method_name, fnname)
 			) {
 				fn_copy = *fn;
-
-				/* if it is 0, no modifiers have been changed */
-				if (alias->modifiers) {
+				if (alias->modifiers & ZEND_ACC_PPP_MASK) {
 					fn_copy.common.fn_flags = alias->modifiers | (fn->common.fn_flags & ~ZEND_ACC_PPP_MASK);
+				} else {
+					fn_copy.common.fn_flags = alias->modifiers | fn->common.fn_flags;
 				}
 
 				lcname = zend_string_tolower(alias->alias);
@@ -2079,7 +2083,11 @@ static void zend_traits_copy_functions(zend_string *fnname, zend_function *fn, z
 					&& fn->common.scope == aliases[i]
 					&& zend_string_equals_ci(alias->trait_method.method_name, fnname)
 				) {
-					fn_copy.common.fn_flags = alias->modifiers | (fn->common.fn_flags & ~ZEND_ACC_PPP_MASK);
+					if (alias->modifiers & ZEND_ACC_PPP_MASK) {
+						fn_copy.common.fn_flags = alias->modifiers | (fn->common.fn_flags & ~ZEND_ACC_PPP_MASK);
+					} else {
+						fn_copy.common.fn_flags = alias->modifiers | fn->common.fn_flags;
+					}
 				}
 				alias_ptr++;
 				alias = *alias_ptr;