diff --git a/src/Type/Regex/RegexGroupParser.php b/src/Type/Regex/RegexGroupParser.php
index a98fb20b42..beea95bce0 100644
--- a/src/Type/Regex/RegexGroupParser.php
+++ b/src/Type/Regex/RegexGroupParser.php
@@ -74,7 +74,7 @@ public function parseGroups(string $regex): ?array
 
 		if (str_contains($modifiers, 'x')) {
 			// in freespacing mode the # character starts a comment and runs until the end of the line
-			$regex = preg_replace('/[^?]#.*/', '', $regex) ?? '';
+			$regex = preg_replace('/(?<!\?)#.*/', '', $regex) ?? '';
 		}
 
 		$rawRegex = $this->regexExpressionHelper->removeDelimitersAndModifiers($regex);
diff --git a/tests/PHPStan/Analyser/nsrt/bug-12242.php b/tests/PHPStan/Analyser/nsrt/bug-12242.php
index cb6d424567..4d065367a2 100644
--- a/tests/PHPStan/Analyser/nsrt/bug-12242.php
+++ b/tests/PHPStan/Analyser/nsrt/bug-12242.php
@@ -30,3 +30,14 @@ function bar(string $str): void
 		assertType('array{string, non-empty-string, string, string}', $matches);
 	}
 }
+
+function foobar(string $str): void
+{
+	$regexp = '/
+		# (
+		([\d,]*)# a comment immediately behind with a closing parenthesis )
+	/x';
+	if (preg_match($regexp, $str, $match)) {
+		assertType('array{string, string}', $match);
+	}
+}