diff --git a/ext/json/json_encoder.c b/ext/json/json_encoder.c
index 1e344cde436ff..f074389c6f38e 100644
--- a/ext/json/json_encoder.c
+++ b/ext/json/json_encoder.c
@@ -677,6 +677,11 @@ zend_result php_json_encode_zval(smart_str *buf, zval *val, int options, php_jso
 			if (Z_OBJCE_P(val)->ce_flags & ZEND_ACC_ENUM) {
 				return php_json_encode_serializable_enum(buf, val, options, encoder);
 			}
+			if (Z_OBJCE_P(val)->ce_flags & ZEND_ACC_NOT_SERIALIZABLE) {
+				if (!(Z_OBJCE_P(val)->ce_flags & ZEND_ACC_ANON_CLASS) || (Z_OBJCE_P(val)->parent && Z_OBJCE_P(val)->parent->ce_flags & ZEND_ACC_NOT_SERIALIZABLE)) {
+					zend_error(E_DEPRECATED, "json_encode() of non-serializable class %s is deprecated", ZSTR_VAL(Z_OBJCE_P(val)->name));
+				}
+			}
 			/* fallthrough -- Non-serializable object */
 			ZEND_FALLTHROUGH;
 		case IS_ARRAY: {
diff --git a/tests/classes/json_encode_non_serializable_deprecated.phpt b/tests/classes/json_encode_non_serializable_deprecated.phpt
new file mode 100644
index 0000000000000..a1673373ef5fd
--- /dev/null
+++ b/tests/classes/json_encode_non_serializable_deprecated.phpt
@@ -0,0 +1,24 @@
+--TEST--
+json_encode() on instances of classes market with ZEND_ACC_NOT_SERIALIZABLE
+--FILE--
+<?php
+function a() { for ($i=0; $i < 10; $i++) { yield $i; }};
+$fn = a(...);
+
+$c1 = new class() extends PDOStatement {};
+$c2 = new class() extends stdClass {};
+$c3 = new class() {};
+
+echo json_encode(a());
+echo json_encode($fn);
+echo json_encode($c1);
+echo json_encode($c2);
+echo json_encode($c3);
+?>
+--EXPECTF--
+Deprecated: json_encode() of non-serializable class Generator is deprecated in %s on line %d
+{}
+Deprecated: json_encode() of non-serializable class Closure is deprecated in %s on line %d
+{}
+Deprecated: json_encode() of non-serializable class PDOStatement@anonymous is deprecated in %s on line %d
+{}{}{}