diff --git a/src/WhitespacesFixerConfig.php b/src/WhitespacesFixerConfig.php
index e558fd6b9c5..d8dd65ba7b9 100644
--- a/src/WhitespacesFixerConfig.php
+++ b/src/WhitespacesFixerConfig.php
@@ -25,8 +25,8 @@ final class WhitespacesFixerConfig
 
     public function __construct(string $indent = '    ', string $lineEnding = "\n")
     {
-        if (!\in_array($indent, ['  ', '    ', "\t"], true)) {
-            throw new \InvalidArgumentException('Invalid "indent" param, expected tab or two or four spaces.');
+        if (!Preg::match('/^(?: +|\t)$/', $indent)) {
+            throw new \InvalidArgumentException('Invalid "indent" param, expected tab or spaces.');
         }
 
         if (!\in_array($lineEnding, ["\n", "\r\n"], true)) {
diff --git a/tests/WhitespacesFixerConfigTest.php b/tests/WhitespacesFixerConfigTest.php
index f6e800e89c1..5d5ca914a95 100644
--- a/tests/WhitespacesFixerConfigTest.php
+++ b/tests/WhitespacesFixerConfigTest.php
@@ -50,12 +50,14 @@ public static function provideFixCases(): iterable
 
         yield ["\t", "\n"];
 
+        yield [str_repeat(' ', 12), "\n"];
+
         yield ['    ', "\r\n"];
 
         yield ["\t", "\r\n"];
 
         yield ['    ', 'asd', 'Invalid "lineEnding" param, expected "\n" or "\r\n".'];
 
-        yield ['std', "\n", 'Invalid "indent" param, expected tab or two or four spaces.'];
+        yield ['std', "\n", 'Invalid "indent" param, expected tab or spaces.'];
     }
 }