diff --git a/NEWS b/NEWS
index 4b34324de64b..0a35a9cb8c24 100644
--- a/NEWS
+++ b/NEWS
@@ -66,6 +66,10 @@ PHP                                                                        NEWS
   . Fixed password_get_info() and password_needs_rehash() accepting malformed
     bcrypt costs. (Ilia Alshanetsky)
 
+- Tidy:
+  . Fixed tidy_repair_string(), tidy_repair_file(), tidy::repairString() and
+    tidy::repairFile() rejecting null for $encoding. (lacatoire)
+
 - Zip:
   . Fixed use-after-free when re-entering ZipArchive during destruction or
     a close warning, and rejected opening streams while closing. (jvoisin)
diff --git a/ext/tidy/tests/tidy_repair_encoding_null.phpt b/ext/tidy/tests/tidy_repair_encoding_null.phpt
new file mode 100644
index 000000000000..e1948724df56
--- /dev/null
+++ b/ext/tidy/tests/tidy_repair_encoding_null.phpt
@@ -0,0 +1,28 @@
+--TEST--
+tidy_repair_string() / tidy_repair_file() accept null for $encoding, as declared
+--EXTENSIONS--
+tidy
+--FILE--
+<?php
+declare(strict_types=1);
+
+$file = __DIR__ . '/tidy_repair_encoding_null.html';
+file_put_contents($file, '<p>test');
+
+var_dump(strlen(tidy_repair_string('<p>test', null, null)) > 0);
+var_dump(strlen(tidy_repair_file($file, null, null)) > 0);
+var_dump(strlen(tidy::repairString('<p>test', null, null)) > 0);
+var_dump(strlen(tidy::repairFile($file, null, null)) > 0);
+
+var_dump(tidy_repair_string('<p>test', null, null) === tidy_repair_string('<p>test'));
+?>
+--CLEAN--
+<?php
+unlink(__DIR__ . '/tidy_repair_encoding_null.html');
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)
+bool(true)
+bool(true)
diff --git a/ext/tidy/tidy.c b/ext/tidy/tidy.c
index 4b9d0cb5d1c7..48e635022328 100644
--- a/ext/tidy/tidy.c
+++ b/ext/tidy/tidy.c
@@ -352,7 +352,7 @@ static void php_tidy_quick_repair(INTERNAL_FUNCTION_PARAMETERS, bool is_file)
 			Z_PARAM_PATH_STR(arg1)
 			Z_PARAM_OPTIONAL
 			Z_PARAM_ARRAY_HT_OR_STR_OR_NULL(config_ht, config_str)
-			Z_PARAM_STRING(enc, enc_len)
+			Z_PARAM_STRING_OR_NULL(enc, enc_len)
 			Z_PARAM_BOOL(use_include_path)
 		ZEND_PARSE_PARAMETERS_END();
 
@@ -364,7 +364,7 @@ static void php_tidy_quick_repair(INTERNAL_FUNCTION_PARAMETERS, bool is_file)
 			Z_PARAM_STR(arg1)
 			Z_PARAM_OPTIONAL
 			Z_PARAM_ARRAY_HT_OR_STR_OR_NULL(config_ht, config_str)
-			Z_PARAM_STRING(enc, enc_len)
+			Z_PARAM_STRING_OR_NULL(enc, enc_len)
 		ZEND_PARSE_PARAMETERS_END();
 
 		data = arg1;