diff --git a/composer.json b/composer.json
index 95feefc..603bc69 100644
--- a/composer.json
+++ b/composer.json
@@ -62,7 +62,7 @@
         "stan": "@phpstan",
         "stan-baseline": "tools/phpstan --generate-baseline",
         "stan-setup": "phive install",
-        "rector-setup": "cp composer.json composer.backup && composer require --dev rector/rector:\"~2.3.1\" && mv composer.backup composer.json",
+        "rector-setup": "cp composer.json composer.backup && composer require --dev rector/rector:\"~2.3.1\" phpstan/phpstan:\"~2.1.40\" && mv composer.backup composer.json",
         "rector-check": "vendor/bin/rector process --dry-run",
         "rector-fix": "vendor/bin/rector process",
         "test": "phpunit"
diff --git a/src/ChronosTime.php b/src/ChronosTime.php
index f066978..629736e 100644
--- a/src/ChronosTime.php
+++ b/src/ChronosTime.php
@@ -122,7 +122,9 @@ protected static function parseString(string $time): int
         $hours = (int)$matches[1];
         $minutes = (int)$matches[2];
         $seconds = (int)($matches[3] ?? 0);
-        $microseconds = (int)substr($matches[4] ?? '', 0, 6);
+        // The fraction is of a second, so pad on the right to microseconds:
+        // without it ".5" reads as 5us instead of 500000 (half a second).
+        $microseconds = (int)str_pad(substr($matches[4] ?? '', 0, 6), 6, '0', STR_PAD_RIGHT);
 
         if ($hours > 24 || $minutes > 59 || $seconds > 59 || $microseconds > 999_999) {
             throw new InvalidArgumentException(sprintf('Time string `%s` contains invalid values.', $time));
diff --git a/tests/TestCase/ChronosTimeTest.php b/tests/TestCase/ChronosTimeTest.php
index 1be8a37..9f8f233 100644
--- a/tests/TestCase/ChronosTimeTest.php
+++ b/tests/TestCase/ChronosTimeTest.php
@@ -53,6 +53,19 @@ public function testConstructFromString(): void
         $this->assertSame('00:59:59.999999', $t->format('H:i:s.u'));
     }
 
+    public function testConstructFromStringWithFractionalSeconds(): void
+    {
+        // The fractional part is a fraction of a second, matching DateTime.
+        $t = new ChronosTime('12:00:00.5');
+        $this->assertSame('12:00:00.500000', $t->format('H:i:s.u'));
+
+        $t = new ChronosTime('12:00:00.05');
+        $this->assertSame('12:00:00.050000', $t->format('H:i:s.u'));
+
+        $t = new ChronosTime('12:00:00.000005');
+        $this->assertSame('12:00:00.000005', $t->format('H:i:s.u'));
+    }
+
     public function testConstructFromInstance(): void
     {
         $t = new ChronosTime(new DateTimeImmutable('23:59:59.999999'));