diff --git a/src/Composer/Package/Loader/RootPackageLoader.php b/src/Composer/Package/Loader/RootPackageLoader.php
index ac3d8f433..536d461ad 100644
--- a/src/Composer/Package/Loader/RootPackageLoader.php
+++ b/src/Composer/Package/Loader/RootPackageLoader.php
@@ -110,6 +110,11 @@ class RootPackageLoader extends ArrayLoader
             }
         }
 
+        $defaultBranch = $this->versionGuesser->getDefaultBranchName($cwd ?: getcwd());
+        if ($defaultBranch && $config['version'] === 'dev-'.$defaultBranch) {
+            $config['default-branch'] = true;
+        }
+
         $realPackage = $package = parent::load($config, $class);
         if ($realPackage instanceof AliasPackage) {
             $realPackage = $package->getAliasOf();
diff --git a/src/Composer/Package/Version/VersionGuesser.php b/src/Composer/Package/Version/VersionGuesser.php
index d3f78e5c0..8b886fc25 100644
--- a/src/Composer/Package/Version/VersionGuesser.php
+++ b/src/Composer/Package/Version/VersionGuesser.php
@@ -110,6 +110,35 @@ class VersionGuesser
         return $versionData;
     }
 
+    /**
+     * Tries to find name of default branch from VCS info
+     *
+     * @param string $path Path to guess into
+     */
+    public function getDefaultBranchName($path)
+    {
+        GitUtil::cleanEnv();
+        if (0 === $this->process->execute('git remote show origin', $output, $path) || 0 === $this->process->execute('git remote show upstream', $output, $path)) {
+            if (preg_match('{^  HEAD branch: (.+)$}m', $output, $match)) {
+                return trim($match[1]);
+            }
+        }
+
+        if (is_dir($path.'/.git')) {
+            return 'master';
+        }
+
+        if (is_dir($path.'/.hg')) {
+            return 'default';
+        }
+
+        if (is_dir($path.'/.svn')) {
+            return 'trunk';
+        }
+
+        return null;
+    }
+
     private function guessGitVersion(array $packageConfig, $path)
     {
         GitUtil::cleanEnv();
@@ -155,16 +184,8 @@ class VersionGuesser
                 $featureVersion = $version;
                 $featurePrettyVersion = $prettyVersion;
 
-                // try to find name of default branch from git info
-                $defaultBranch = null;
-                if (0 === $this->process->execute('git remote show origin', $output) || 0 === $this->process->execute('git remote show upstream', $output)) {
-                    if (preg_match('{^  HEAD branch: (.+)$}m', $output, $match)) {
-                        $defaultBranch = trim($match[1]);
-                    }
-                }
-
                 // try to find the best (nearest) version branch to assume this feature's version
-                $result = $this->guessFeatureVersion($packageConfig, $version, $branches, 'git rev-list %candidate%..%branch%', $path, $defaultBranch);
+                $result = $this->guessFeatureVersion($packageConfig, $version, $branches, 'git rev-list %candidate%..%branch%', $path);
                 $version = $result['version'];
                 $prettyVersion = $result['pretty_version'];
             }
@@ -231,7 +252,7 @@ class VersionGuesser
             $branches = array_keys($driver->getBranches());
 
             // try to find the best (nearest) version branch to assume this feature's version
-            $result = $this->guessFeatureVersion($packageConfig, $version, $branches, 'hg log -r "not ancestors(\'%candidate%\') and ancestors(\'%branch%\')" --template "{node}\\n"', $path, 'default');
+            $result = $this->guessFeatureVersion($packageConfig, $version, $branches, 'hg log -r "not ancestors(\'%candidate%\') and ancestors(\'%branch%\')" --template "{node}\\n"', $path);
             $result['commit'] = '';
             $result['feature_version'] = $version;
             $result['feature_pretty_version'] = $version;
@@ -240,7 +261,7 @@ class VersionGuesser
         }
     }
 
-    private function guessFeatureVersion(array $packageConfig, $version, array $branches, $scmCmdline, $path, $defaultBranch)
+    private function guessFeatureVersion(array $packageConfig, $version, array $branches, $scmCmdline, $path)
     {
         $prettyVersion = $version;
 
@@ -262,6 +283,8 @@ class VersionGuesser
                 return array('version' => $version, 'pretty_version' => $prettyVersion);
             }
 
+            $defaultBranch = $this->getDefaultBranchName($path);
+
             foreach ($branches as $candidate) {
                 // do not compare against itself or other feature branches
                 if ($candidate === $branch || !preg_match('{^(' . $nonFeatureBranches . ($defaultBranch ? '|'.preg_quote($defaultBranch) : '').'|master|trunk|default|develop|\d+\..+)$}', $candidate, $match)) {
diff --git a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
index 93cde83f5..e5aebd1d0 100644
--- a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
@@ -105,6 +105,8 @@ class RootPackageLoaderTest extends TestCase
                 'pretty_version' => '3.0-dev',
                 'commit' => 'aabbccddee',
             ));
+        $versionGuesser->getDefaultBranchName(Argument::cetera())
+            ->willReturn('main');
         $config = new Config;
         $config->merge(array('repositories' => array('packagist' => false)));
         $loader = new RootPackageLoader($manager->reveal(), $config, null, $versionGuesser->reveal());
@@ -113,6 +115,28 @@ class RootPackageLoaderTest extends TestCase
         $this->assertEquals('3.0-dev', $package->getPrettyVersion());
     }
 
+    public function testDefaultBranchIsSetForRootPackageInDefaultBranch()
+    {
+        // see #6845
+        $manager = $this->prophesize('\\Composer\\Repository\\RepositoryManager');
+        $versionGuesser = $this->prophesize('\\Composer\\Package\\Version\\VersionGuesser');
+        $versionGuesser->guessVersion(Argument::cetera())
+            ->willReturn(array(
+                'name' => 'A',
+                'version' => 'dev-main',
+                'pretty_version' => 'dev-main',
+                'commit' => 'aabbccddee',
+            ));
+        $versionGuesser->getDefaultBranchName(Argument::cetera())
+            ->willReturn('main');
+        $config = new Config;
+        $config->merge(array('repositories' => array('packagist' => false)));
+        $loader = new RootPackageLoader($manager->reveal(), $config, null, $versionGuesser->reveal());
+        $package = $loader->load(array());
+
+        $this->assertTrue($package->isDefaultBranch());
+    }
+
     public function testFeatureBranchPrettyVersion()
     {
         if (!function_exists('proc_open')) {
@@ -147,6 +171,17 @@ class RootPackageLoaderTest extends TestCase
         $executor
             ->expects($this->at(1))
             ->method('execute')
+            ->willReturnCallback(function ($command, &$output) use ($self) {
+                $self->assertEquals('git remote show origin', $command);
+                $output = "  HEAD branch: master";
+
+                return 0;
+            })
+        ;
+
+        $executor
+            ->expects($this->at(2))
+            ->method('execute')
             ->willReturnCallback(function ($command, &$output) use ($self) {
                 $self->assertEquals('git rev-list master..latest-production', $command);
                 $output = "";