Use --tags to get non-annotated tags as well.

src/Composer/Package/Loader/RootPackageLoader.php

@@ -185,7 +185,7 @@ class RootPackageLoader extends ArrayLoader
     private function guessGitVersion(array $config)
     {
         // try to fetch current version from git branch as a tag
-        if (0 === $this->process->execute('git describe --exact-match', $output)) {
+        if (0 === $this->process->execute('git describe --exact-match --tags', $output)) {
             return $this->versionParser->normalize(rtrim($output));
         }
 

tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php

@@ -69,7 +69,7 @@ class RootPackageLoaderTest extends \PHPUnit_Framework_TestCase
 
         /* Can do away with this mock object when https://github.com/sebastianbergmann/phpunit-mock-objects/issues/81 is fixed */
         $processExecutor = new ProcessExecutorMock(function($command, &$output = null, $cwd = null) use ($self) {
-            $self->assertEquals('git describe --exact-match', $command);
+            $self->assertEquals('git describe --exact-match --tags', $command);
 
             $output = "v2.0.5-alpha2";