Updated $branchAliasVersion set based on @Seldaek's suggestion.

src/Composer/Compiler.php

@@ -50,13 +50,7 @@ class Compiler
         if ($process->run() != 0) {
             throw new \RuntimeException('Can\'t run git log. You must ensure to run compile from composer git repository clone and that git binary is available.');
         }
-        $localConfig = __DIR__.'/../../composer.json';
-        $file = new JsonFile($localConfig);
-        $localConfig = $file->read();
 
-        if (isset($localConfig['extra']['branch-alias']['dev-master'])) {
-            $this->branchAliasVersion = $localConfig['extra']['branch-alias']['dev-master'];
-        }
         $date = new \DateTime(trim($process->getOutput()));
         $date->setTimezone(new \DateTimeZone('UTC'));
         $this->versionDate = $date->format('Y-m-d H:i:s');
@@ -64,6 +58,14 @@ class Compiler
         $process = new Process('git describe --tags HEAD');
         if ($process->run() == 0) {
             $this->version = trim($process->getOutput());
+        } else {
+            // get branch-alias defined in composer.json for dev-master (if any)
+            $localConfig = __DIR__.'/../../composer.json';
+            $file = new JsonFile($localConfig);
+            $localConfig = $file->read();
+            if (isset($localConfig['extra']['branch-alias']['dev-master'])) {
+                $this->branchAliasVersion = $localConfig['extra']['branch-alias']['dev-master'];
+            }
         }
 
         $phar = new \Phar($pharFile, 0, 'composer.phar');