diff --git a/src/PhantomInstaller/Installer.php b/src/PhantomInstaller/Installer.php
index 90f0bb4..a015c05 100644
--- a/src/PhantomInstaller/Installer.php
+++ b/src/PhantomInstaller/Installer.php
@@ -528,18 +528,16 @@ public function getCdnUrl($version)
             $url = static::PHANTOMJS_CDNURL_DEFAULT;
         }
 
-        $url = strtolower($url);
-
-        // add version to URL when using "github.com/medium/phantomjs"
-        if (strpos($url, 'github.com/medium/phantomjs') !== false) {
-            return 'https://github.com/medium/phantomjs/releases/download/v' . $version . '/';
-        }
-
         // add slash at the end of the URL, if missing
         if ($url[strlen($url) - 1] != '/') {
             $url .= '/';
         }
 
+        // add version to URL when using "github.com/medium/phantomjs"
+        if (substr(strtolower($url), -28) == 'github.com/medium/phantomjs/') {
+            $url .= 'releases/download/v' . $version . '/';
+        }
+
         return $url;
     }
 
diff --git a/tests/InstallerTest.php b/tests/InstallerTest.php
index aade110..3114548 100644
--- a/tests/InstallerTest.php
+++ b/tests/InstallerTest.php
@@ -110,10 +110,18 @@ public function testSpecialGithubPatternForCdnUrl()
     {
         $this->setUpForGetCdnUrl();
         $version = '1.0.0';
-        $configuredCdnUrl = 'https://github.com/medium/phantomjs';
+
+        // Test rewrite for the Medium url as documented
+        $configuredCdnUrl = 'https://github.com/Medium/phantomjs';
+        $_ENV['PHANTOMJS_CDNURL'] = $configuredCdnUrl;
+        $cdnurl = $this->object->getCdnUrl($version);
+        $this->assertSame($configuredCdnUrl . '/releases/download/v' . $version . '/', $cdnurl);
+
+        // Test that a longer url is not rewritten
+        $configuredCdnUrl = 'https://github.com/Medium/phantomjs/releases/download/v1.9.19/';
         $_ENV['PHANTOMJS_CDNURL'] = $configuredCdnUrl;
         $cdnurl = $this->object->getCdnUrl($version);
-        $this->assertSame('https://github.com/medium/phantomjs/releases/download/v' . $version . '/', $cdnurl);
+        $this->assertSame($configuredCdnUrl, $cdnurl);
     }
 
     /**