diff --git a/src/functions.php b/src/functions.php
index b5f489a1e..08670def2 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -16,7 +16,7 @@ function isAbsolutePath($path)
     $regex = '%^(?<wrappers>(?:[[:print:]]{2,}://)*)';
 
     // Optional root prefix.
-    $regex .= '(?<root>(?:[[:alpha:]]:/|/)?)';
+    $regex .= '(?<root>(?:[[:alpha:]]:[\\\/]|[\\\/])?)';
 
     // Actual path.
     $regex .= '(?<path>(?:[[:print:]]*))$%';
diff --git a/tests/Config/PluginTest.php b/tests/Config/PluginTest.php
index 9604d4504..304f10b39 100644
--- a/tests/Config/PluginTest.php
+++ b/tests/Config/PluginTest.php
@@ -4,7 +4,6 @@ namespace Psalm\Tests\Config;
 use function define;
 use function defined;
 use const DIRECTORY_SEPARATOR;
-use const PHP_OS;
 use function dirname;
 use function get_class;
 use function getcwd;
@@ -18,7 +17,6 @@ use Psalm\PluginRegistrationSocket;
 use Psalm\Tests\Internal\Provider;
 use Psalm\Tests\TestConfig;
 use function sprintf;
-use function stripos;
 
 class PluginTest extends \Psalm\Tests\TestCase
 {
@@ -821,10 +819,6 @@ class PluginTest extends \Psalm\Tests\TestCase
      */
     public function testPluginFilenameCanBeAbsolute()
     {
-        if ($this->runningOnWindows()) {
-            $this->markTestIncomplete('Test fails on Windows - see https://github.com/vimeo/psalm/issues/1913');
-        }
-
         $this->project_analyzer = $this->getProjectAnalyzerWithConfig(
             TestConfig::loadFromXML(
                 dirname(__DIR__, 2) . DIRECTORY_SEPARATOR,
@@ -871,9 +865,4 @@ class PluginTest extends \Psalm\Tests\TestCase
 
         $this->project_analyzer->getCodebase()->config->initializePlugins($this->project_analyzer);
     }
-
-    private function runningOnWindows(): bool
-    {
-        return stripos(PHP_OS, 'WIN') === 0;
-    }
 }
diff --git a/tests/IsAbsolutePathTest.php b/tests/IsAbsolutePathTest.php
index 4f03a18df..02c63ab7b 100644
--- a/tests/IsAbsolutePathTest.php
+++ b/tests/IsAbsolutePathTest.php
@@ -29,6 +29,10 @@ class IsAbsolutePathTest extends TestCase
             ['relative/path/to/something', false],
             ['relative/path/to/something/file.php', false],
             ['c:/path/to/something', true],
+            ['C:\path\to\something', true],
+            ['C:\path/to\something', true],
+            ['\path\to\something', true],
+            ['C:\path/to\..\..\something', true],
             ['file://c:/path/to/something', true],
             ['zlib://c:/path/to/something', true],
         ];