diff --git a/src/ClassMapGenerator.php b/src/ClassMapGenerator.php
index 31ef653..5966f86 100644
--- a/src/ClassMapGenerator.php
+++ b/src/ClassMapGenerator.php
@@ -152,7 +152,7 @@ public function scanPaths($path, ?string $excluded = null, string $autoloadType
                 $filePath = $cwd . '/' . $filePath;
                 $filePath = self::normalizePath($filePath);
             } else {
-                $filePath = Preg::replace('{(?<!:)[\\\\/]{2,}}', '/', $filePath);
+                $filePath = Preg::replace('{(?<![:/])[\\\\/]{2,}}', '/', $filePath);
             }
 
             if ('' === $filePath) {
diff --git a/tests/ClassMapGeneratorTest.php b/tests/ClassMapGeneratorTest.php
index 5c0f7e6..69be72e 100644
--- a/tests/ClassMapGeneratorTest.php
+++ b/tests/ClassMapGeneratorTest.php
@@ -261,6 +261,27 @@ public function url_stat(string $path, int $flags)
         );
     }
 
+    public function testStreamWrapperWithAbsolutePath(): void
+    {
+        if ('\\' === \DIRECTORY_SEPARATOR) {
+            self::markTestSkipped('Absolute paths start with a drive letter on Windows');
+        }
+
+        $archive = realpath(sys_get_temp_dir()).'/class-map-generator-'.bin2hex(random_bytes(4)).'.tar';
+        $phar = new \PharData($archive);
+        $phar->addFromString('src/Foo.php', '<?php namespace Acme; class Foo {}');
+        unset($phar);
+
+        try {
+            self::assertSame(
+                ['Acme\\Foo' => 'phar://'.$archive.'/src/Foo.php'],
+                ClassMapGenerator::createMap('phar://'.$archive.'/src')
+            );
+        } finally {
+            unlink($archive);
+        }
+    }
+
     public function testAmbiguousReference(): void
     {
         $tempDir = self::getUniqueTmpDirectory();