diff --git a/stubs/core.stub b/stubs/core.stub
index 652fed707d..ff0980db3d 100644
--- a/stubs/core.stub
+++ b/stubs/core.stub
@@ -69,7 +69,7 @@ function str_shuffle(string $string): string {}
 
 /**
  * @param array<mixed> $result
- * @param-out array<int|string, array<mixed>|string> $result
+ * @param-out ($string is lowercase-string ? array<int|string, array<mixed>|lowercase-string> : array<int|string, array<mixed>|string>) $result
  */
 function parse_str(string $string, array &$result): void {}
 
diff --git a/tests/PHPStan/Analyser/nsrt/lowercase-string-parse.php b/tests/PHPStan/Analyser/nsrt/lowercase-string-parse.php
new file mode 100644
index 0000000000..ba95e975da
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/lowercase-string-parse.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace LowercaseStringParseStr;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	/**
+	 * @param lowercase-string $lowercase
+	 */
+	public function parse(string $lowercase, string $string): void
+	{
+		$a = [];
+		parse_str($lowercase, $a);
+
+		if (array_key_exists('foo', $a)) {
+			$value = $a['foo'];
+			if (\is_string($value)) {
+				assertType('lowercase-string', $value);
+			}
+		}
+
+		$b = [];
+		parse_str($string, $b);
+
+		if (array_key_exists('foo', $b)) {
+			$value = $b['foo'];
+			if (\is_string($value)) {
+				assertType('string', $value);
+			}
+		}
+	}
+
+}