diff --git a/Zend/tests/typehints/mixed.phpt b/Zend/tests/typehints/mixed.phpt
new file mode 100644
index 0000000000000..dac5f91b65ed0
--- /dev/null
+++ b/Zend/tests/typehints/mixed.phpt
@@ -0,0 +1,31 @@
+--TEST--
+Test various types passed to mixed type.
+--FILE--
+<?php
+
+$types = [
+	NULL,
+	TRUE,
+	123,
+	123.456,
+	'php',
+	new stdClass,
+	fopen(__FILE__, 'r'),
+];
+
+function test(mixed $arg) {
+	var_dump($arg);
+}
+
+foreach ($types as $type) {
+	test($type);
+}
+--EXPECTF--
+NULL
+bool(true)
+int(123)
+float(123.456)
+string(3) "php"
+object(stdClass)#%d (%d) {
+}
+resource(%d) of type (stream)
diff --git a/Zend/tests/typehints/mixed_inheritance.phpt b/Zend/tests/typehints/mixed_inheritance.phpt
new file mode 100644
index 0000000000000..bee3071209f73
--- /dev/null
+++ b/Zend/tests/typehints/mixed_inheritance.phpt
@@ -0,0 +1,27 @@
+--TEST--
+Test mixed variance in inheritance.
+--FILE--
+<?php
+
+class Foo {
+	function test(mixed $arg): mixed
+	{
+		return $arg;
+	}
+}
+
+class Bar extends Foo {
+	function test($arg) {
+		return parent::test($arg);
+	}
+}
+
+class Baz extends bar {
+	function test(mixed $arg): mixed {
+		return parent::test($arg);
+	}
+}
+
+var_dump((new Baz())->test(123));
+--EXPECT--
+int(123)
diff --git a/Zend/tests/typehints/mixed_nullable_parameter.phpt b/Zend/tests/typehints/mixed_nullable_parameter.phpt
new file mode 100644
index 0000000000000..922f394fb53e0
--- /dev/null
+++ b/Zend/tests/typehints/mixed_nullable_parameter.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Test nullable mixed parameter type.
+--FILE--
+<?php
+
+function test(?mixed $arg) {
+}
+
+--EXPECTF--
+Fatal error: Mixed type cannot be nullable in %smixed_nullable_parameter.php on line %d
diff --git a/Zend/tests/typehints/mixed_nullable_return.phpt b/Zend/tests/typehints/mixed_nullable_return.phpt
new file mode 100644
index 0000000000000..1f64fecd9ca05
--- /dev/null
+++ b/Zend/tests/typehints/mixed_nullable_return.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Test nullable mixed return type.
+--FILE--
+<?php
+
+function test($arg): ?mixed {
+}
+
+--EXPECTF--
+Fatal error: Mixed type cannot be nullable in %smixed_nullable_return.php on line %d
diff --git a/Zend/zend_API.c b/Zend/zend_API.c
index b05c5a96d4757..912d6eb47cdb2 100644
--- a/Zend/zend_API.c
+++ b/Zend/zend_API.c
@@ -128,6 +128,8 @@ ZEND_API char *zend_get_type_by_const(int type) /* {{{ */
 			return "void";
 		case _IS_NUMBER:
 			return "number";
+		case IS_MIXED:
+			return "mixed";
 		default:
 			return "unknown";
 	}
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index 310fac9cc973e..6a3ca32eb2de1 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -176,6 +176,7 @@ static const struct reserved_class_name reserved_class_names[] = {
 	{ZEND_STRL("void")},
 	{ZEND_STRL("iterable")},
 	{ZEND_STRL("object")},
+	{ZEND_STRL("mixed")},
 	{NULL, 0}
 };
 
@@ -222,6 +223,7 @@ static const builtin_type_info builtin_types[] = {
 	{ZEND_STRL("void"), IS_VOID},
 	{ZEND_STRL("iterable"), IS_ITERABLE},
 	{ZEND_STRL("object"), IS_OBJECT},
+	{ZEND_STRL("mixed"), IS_MIXED},
 	{NULL, 0, IS_UNDEF}
 };
 
@@ -5486,6 +5488,10 @@ void zend_compile_params(zend_ast *ast, zend_ast *return_type_ast) /* {{{ */
 			zend_error_noreturn(E_COMPILE_ERROR, "Void type cannot be nullable");
 		}
 
+		if (ZEND_TYPE_CODE(arg_infos->type) == IS_MIXED && ZEND_TYPE_ALLOW_NULL(arg_infos->type)) {
+			zend_error_noreturn(E_COMPILE_ERROR, "Mixed type cannot be nullable");
+		}
+
 		arg_infos++;
 		op_array->fn_flags |= ZEND_ACC_HAS_RETURN_TYPE;
 	} else {
@@ -5581,6 +5587,10 @@ void zend_compile_params(zend_ast *ast, zend_ast *return_type_ast) /* {{{ */
 				zend_error_noreturn(E_COMPILE_ERROR, "void cannot be used as a parameter type");
 			}
 
+			if (ZEND_TYPE_CODE(arg_info->type) == IS_MIXED && ZEND_TYPE_ALLOW_NULL(arg_info->type)) {
+				zend_error_noreturn(E_COMPILE_ERROR, "Mixed type cannot be nullable");
+			}
+
 			if (type_ast->kind == ZEND_AST_TYPE) {
 				if (ZEND_TYPE_CODE(arg_info->type) == IS_ARRAY) {
 					if (default_ast && !has_null_default
diff --git a/Zend/zend_execute.c b/Zend/zend_execute.c
index 55c24f31e98b4..60004fba5b79d 100644
--- a/Zend/zend_execute.c
+++ b/Zend/zend_execute.c
@@ -945,6 +945,8 @@ static zend_always_inline zend_bool zend_check_type(
 	} else if (ZEND_TYPE_CODE(type) == _IS_BOOL &&
 			   EXPECTED(Z_TYPE_P(arg) == IS_FALSE || Z_TYPE_P(arg) == IS_TRUE)) {
 		return 1;
+	} else if (ZEND_TYPE_CODE(type) == IS_MIXED) {
+		return 1;
 	} else {
 		return zend_verify_scalar_type_hint(ZEND_TYPE_CODE(type), arg,
 			is_return_type ? ZEND_RET_USES_STRICT_TYPES() : ZEND_ARG_USES_STRICT_TYPES());
diff --git a/Zend/zend_inheritance.c b/Zend/zend_inheritance.c
index be605a49de6c2..cc7f3c8c2c0ec 100644
--- a/Zend/zend_inheritance.c
+++ b/Zend/zend_inheritance.c
@@ -253,7 +253,10 @@ static int zend_do_perform_arg_type_hint_check(const zend_function *fe, zend_arg
 	}
 
 	if (!ZEND_TYPE_IS_SET(proto_arg_info->type)) {
-		/* Child defines a type, but parent doesn't, violates LSP */
+		/* Child defines a type, but parent doesn't, violates LSP, unless it's a mixed type */
+		if (ZEND_TYPE_CODE(fe_arg_info->type) == IS_MIXED) {
+			return 1;
+		}
 		return 0;
 	}
 
@@ -359,6 +362,9 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 	if (proto->common.fn_flags & ZEND_ACC_HAS_RETURN_TYPE) {
 		/* Removing a return type is not valid. */
 		if (!(fe->common.fn_flags & ZEND_ACC_HAS_RETURN_TYPE)) {
+			if (ZEND_TYPE_CODE(proto->common.arg_info[-1].type) == IS_MIXED) {
+				return 1;
+			}
 			return 0;
 		}
 
diff --git a/Zend/zend_types.h b/Zend/zend_types.h
index 59b0af1a4a818..2cb8eadc19569 100644
--- a/Zend/zend_types.h
+++ b/Zend/zend_types.h
@@ -407,6 +407,7 @@ struct _zend_ast_ref {
 #define IS_ITERABLE					18
 #define IS_VOID						19
 #define _IS_NUMBER					20
+#define IS_MIXED					21
 
 static zend_always_inline zend_uchar zval_get_type(const zval* pz) {
 	return pz->u1.v.type;