diff --git a/src/Composer/Command/DiagnoseCommand.php b/src/Composer/Command/DiagnoseCommand.php
index e2301c813..16add1e33 100644
--- a/src/Composer/Command/DiagnoseCommand.php
+++ b/src/Composer/Command/DiagnoseCommand.php
@@ -286,7 +286,7 @@ EOT
     {
         $this->getIO()->setAuthentication($domain, $token, 'x-oauth-basic');
         try {
-            $url = $domain === 'github.com' ? 'https://api.'.$domain.'/user/repos' : 'https://'.$domain.'/api/v3/user/repos';
+            $url = $domain === 'github.com' ? 'https://api.'.$domain.'/' : 'https://'.$domain.'/api/v3/';
 
             return $this->rfs->getContents($domain, $url, false, array(
                 'retry-auth-failure' => false,
diff --git a/src/Composer/Util/GitHub.php b/src/Composer/Util/GitHub.php
index 10cb2dc71..a8fd3dc70 100644
--- a/src/Composer/Util/GitHub.php
+++ b/src/Composer/Util/GitHub.php
@@ -102,7 +102,7 @@ class GitHub
         $this->io->setAuthentication($originUrl, $token, 'x-oauth-basic');
 
         try {
-            $apiUrl = ('github.com' === $originUrl) ? 'api.github.com' : $originUrl . '/api/v3';
+            $apiUrl = ('github.com' === $originUrl) ? 'api.github.com/' : $originUrl . '/api/v3/';
 
             $this->remoteFilesystem->getContents($originUrl, 'https://'. $apiUrl, false, array(
                 'retry-auth-failure' => false,
diff --git a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
index f1e51fefd..30179a1a9 100644
--- a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
@@ -78,7 +78,7 @@ class GitHubDriverTest extends TestCase
 
         $remoteFilesystem->expects($this->at(1))
             ->method('getContents')
-            ->with($this->equalTo('github.com'), $this->equalTo('https://api.github.com'), $this->equalTo(false))
+            ->with($this->equalTo('github.com'), $this->equalTo('https://api.github.com/'), $this->equalTo(false))
             ->will($this->returnValue('{}'));
 
         $remoteFilesystem->expects($this->at(2))
diff --git a/tests/Composer/Test/Util/GitHubTest.php b/tests/Composer/Test/Util/GitHubTest.php
index ff245004a..c7d4061e1 100644
--- a/tests/Composer/Test/Util/GitHubTest.php
+++ b/tests/Composer/Test/Util/GitHubTest.php
@@ -50,7 +50,7 @@ class GitHubTest extends \PHPUnit_Framework_TestCase
             ->method('getContents')
             ->with(
                 $this->equalTo($this->origin),
-                $this->equalTo(sprintf('https://api.%s', $this->origin)),
+                $this->equalTo(sprintf('https://api.%s/', $this->origin)),
                 $this->isFalse(),
                 $this->anything()
             )