diff --git a/NEWS b/NEWS
index 18d931bccded..d8242f50594c 100644
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,8 @@ PHP                                                                        NEWS
   . Added IntlNumberRangeFormatter class to format an interval of two numbers
     with a given skeleton, locale, collapse type and identity fallback.
     (BogdanUngureanu)
+  . Fixed bug GH-20426 (Spoofchecker::setRestrictionLevel() error message
+    suggests missing constants). (DanielEScherzer)
 
 - Fibers:
   . Fixed bug GH-20483 (ASAN stack overflow with fiber.stack_size INI
diff --git a/ext/intl/spoofchecker/spoofchecker_main.cpp b/ext/intl/spoofchecker/spoofchecker_main.cpp
index ddbf02a0d3de..e49ddec87a3c 100644
--- a/ext/intl/spoofchecker/spoofchecker_main.cpp
+++ b/ext/intl/spoofchecker/spoofchecker_main.cpp
@@ -162,8 +162,8 @@ U_CFUNC PHP_METHOD(Spoofchecker, setRestrictionLevel)
 			USPOOF_MINIMALLY_RESTRICTIVE != level &&
 			USPOOF_UNRESTRICTIVE != level) {
 		zend_argument_value_error(1, "must be one of Spoofchecker::ASCII, Spoofchecker::SINGLE_SCRIPT_RESTRICTIVE, "
-			"Spoofchecker::SINGLE_HIGHLY_RESTRICTIVE, Spoofchecker::SINGLE_MODERATELY_RESTRICTIVE, "
-			"Spoofchecker::SINGLE_MINIMALLY_RESTRICTIVE, or Spoofchecker::UNRESTRICTIVE");
+			"Spoofchecker::HIGHLY_RESTRICTIVE, Spoofchecker::MODERATELY_RESTRICTIVE, "
+			"Spoofchecker::MINIMALLY_RESTRICTIVE, or Spoofchecker::UNRESTRICTIVE");
 		RETURN_THROWS();
 	}
 
diff --git a/ext/intl/tests/spoofchecker_unknown_restriction_level.phpt b/ext/intl/tests/spoofchecker_unknown_restriction_level.phpt
index e8ed48d60a3e..6b7e9474755d 100644
--- a/ext/intl/tests/spoofchecker_unknown_restriction_level.phpt
+++ b/ext/intl/tests/spoofchecker_unknown_restriction_level.phpt
@@ -20,4 +20,4 @@ try {
 
 ?>
 --EXPECT--
-Spoofchecker::setRestrictionLevel(): Argument #1 ($level) must be one of Spoofchecker::ASCII, Spoofchecker::SINGLE_SCRIPT_RESTRICTIVE, Spoofchecker::SINGLE_HIGHLY_RESTRICTIVE, Spoofchecker::SINGLE_MODERATELY_RESTRICTIVE, Spoofchecker::SINGLE_MINIMALLY_RESTRICTIVE, or Spoofchecker::UNRESTRICTIVE
+Spoofchecker::setRestrictionLevel(): Argument #1 ($level) must be one of Spoofchecker::ASCII, Spoofchecker::SINGLE_SCRIPT_RESTRICTIVE, Spoofchecker::HIGHLY_RESTRICTIVE, Spoofchecker::MODERATELY_RESTRICTIVE, Spoofchecker::MINIMALLY_RESTRICTIVE, or Spoofchecker::UNRESTRICTIVE
diff --git a/ext/reflection/php_reflection.stub.php b/ext/reflection/php_reflection.stub.php
index be372ac72991..91c70d6ffdb1 100644
--- a/ext/reflection/php_reflection.stub.php
+++ b/ext/reflection/php_reflection.stub.php
@@ -226,7 +226,7 @@ public function getPrototype(): ReflectionMethod {}
     public function hasPrototype(): bool {}
 
     /** @tentative-return-type */
-    #[\Deprecated(since: '8.5', message: "as it has no effect")]
+    #[\Deprecated(since: '8.5', message: "as it has no effect since PHP 8.1")]
     public function setAccessible(bool $accessible): void {}
 }
 
@@ -543,7 +543,7 @@ public function getDeclaringClass(): ReflectionClass {}
     public function getDocComment(): string|false {}
 
     /** @tentative-return-type */
-    #[\Deprecated(since: '8.5', message: "as it has no effect")]
+    #[\Deprecated(since: '8.5', message: "as it has no effect since PHP 8.1")]
     public function setAccessible(bool $accessible): void {}
 
     /** @tentative-return-type */
diff --git a/ext/reflection/php_reflection_arginfo.h b/ext/reflection/php_reflection_arginfo.h
index d1f1ffed0cfb..62275423b3ca 100644
--- a/ext/reflection/php_reflection_arginfo.h
+++ b/ext/reflection/php_reflection_arginfo.h
@@ -1,5 +1,5 @@
 /* This is a generated file, edit the .stub.php file instead.
- * Stub hash: 576229f7a0c4afd2f8902db6ce87daa51256965e */
+ * Stub hash: fd645a0b0db39d94ca25b39ffe64d7f05bad6bea */
 
 ZEND_BEGIN_ARG_WITH_TENTATIVE_RETURN_TYPE_INFO_EX(arginfo_class_Reflection_getModifierNames, 0, 1, IS_ARRAY, 0)
 	ZEND_ARG_TYPE_INFO(0, modifiers, IS_LONG, 0)
@@ -1497,7 +1497,7 @@ static zend_class_entry *register_class_ReflectionMethod(zend_class_entry *class
 	zend_attribute *attribute_Deprecated_func_setaccessible_0 = zend_add_function_attribute(zend_hash_str_find_ptr(&class_entry->function_table, "setaccessible", sizeof("setaccessible") - 1), ZSTR_KNOWN(ZEND_STR_DEPRECATED_CAPITALIZED), 2);
 	ZVAL_STR(&attribute_Deprecated_func_setaccessible_0->args[0].value, ZSTR_KNOWN(ZEND_STR_8_DOT_5));
 	attribute_Deprecated_func_setaccessible_0->args[0].name = ZSTR_KNOWN(ZEND_STR_SINCE);
-	zend_string *attribute_Deprecated_func_setaccessible_0_arg1_str = zend_string_init("as it has no effect", strlen("as it has no effect"), 1);
+	zend_string *attribute_Deprecated_func_setaccessible_0_arg1_str = zend_string_init("as it has no effect since PHP 8.1", strlen("as it has no effect since PHP 8.1"), 1);
 	ZVAL_STR(&attribute_Deprecated_func_setaccessible_0->args[1].value, attribute_Deprecated_func_setaccessible_0_arg1_str);
 	attribute_Deprecated_func_setaccessible_0->args[1].name = ZSTR_KNOWN(ZEND_STR_MESSAGE);
 
@@ -1662,7 +1662,7 @@ static zend_class_entry *register_class_ReflectionProperty(zend_class_entry *cla
 	zend_attribute *attribute_Deprecated_func_setaccessible_0 = zend_add_function_attribute(zend_hash_str_find_ptr(&class_entry->function_table, "setaccessible", sizeof("setaccessible") - 1), ZSTR_KNOWN(ZEND_STR_DEPRECATED_CAPITALIZED), 2);
 	ZVAL_STR(&attribute_Deprecated_func_setaccessible_0->args[0].value, ZSTR_KNOWN(ZEND_STR_8_DOT_5));
 	attribute_Deprecated_func_setaccessible_0->args[0].name = ZSTR_KNOWN(ZEND_STR_SINCE);
-	zend_string *attribute_Deprecated_func_setaccessible_0_arg1_str = zend_string_init("as it has no effect", strlen("as it has no effect"), 1);
+	zend_string *attribute_Deprecated_func_setaccessible_0_arg1_str = zend_string_init("as it has no effect since PHP 8.1", strlen("as it has no effect since PHP 8.1"), 1);
 	ZVAL_STR(&attribute_Deprecated_func_setaccessible_0->args[1].value, attribute_Deprecated_func_setaccessible_0_arg1_str);
 	attribute_Deprecated_func_setaccessible_0->args[1].name = ZSTR_KNOWN(ZEND_STR_MESSAGE);
 
diff --git a/ext/reflection/tests/ReflectionMethod_setAccessible.phpt b/ext/reflection/tests/ReflectionMethod_setAccessible.phpt
index ba4864d28ed8..be720a4044c7 100644
--- a/ext/reflection/tests/ReflectionMethod_setAccessible.phpt
+++ b/ext/reflection/tests/ReflectionMethod_setAccessible.phpt
@@ -47,13 +47,13 @@ A::aProtected
 A::aProtectedStatic
 A::aProtectedStatic
 
-Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionMethod::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 A::aPrivate
 A::aPrivate
 A::aPrivateStatic
diff --git a/ext/reflection/tests/ReflectionProperty_setAccessible.phpt b/ext/reflection/tests/ReflectionProperty_setAccessible.phpt
index b63ab38c1598..5ccc1366060b 100644
--- a/ext/reflection/tests/ReflectionProperty_setAccessible.phpt
+++ b/ext/reflection/tests/ReflectionProperty_setAccessible.phpt
@@ -96,13 +96,13 @@ string(1) "f"
 string(1) "g"
 string(1) "h"
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 string(1) "e"
 string(1) "f"
 string(1) "g"
@@ -120,11 +120,11 @@ string(1) "e"
 string(1) "f"
 string(1) "g"
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 
-Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect in %s on line %d
+Deprecated: Method ReflectionProperty::setAccessible() is deprecated since 8.5, as it has no effect since PHP 8.1 in %s on line %d
 string(1) "e"
 string(1) "f"
 string(1) "g"