diff --git a/src/Composer/Repository/Vcs/FossilDriver.php b/src/Composer/Repository/Vcs/FossilDriver.php
index 961e696bf..0479c70a6 100644
--- a/src/Composer/Repository/Vcs/FossilDriver.php
+++ b/src/Composer/Repository/Vcs/FossilDriver.php
@@ -34,56 +34,76 @@ class FossilDriver extends VcsDriver
      */
     public function initialize()
     {
-        if (Filesystem::isLocalPath($this->url)) {
+        // Make sure fossil is installed and reachable.
+        $this->checkFossil();
+
+        // Ensure we are allowed to use this URL by config.
+        $this->config->prohibitUrlByConfig($this->url, $this->io);
+
+        // Only if url points to a locally accessible directory, assume it's the checkout directory.
+        // Otherwise, it should be something fossil can clone from.
+        if (Filesystem::isLocalPath($this->url) && is_dir($this->url)) {
             $this->checkoutDir = $this->url;
         } else {
-            $this->repoFile = $this->config->get('cache-repo-dir') . '/' . preg_replace('{[^a-z0-9]}i', '-', $this->url) . '.fossil';
-            $this->checkoutDir = $this->config->get('cache-vcs-dir') . '/' . preg_replace('{[^a-z0-9]}i', '-', $this->url) . '/';
-
-            $fs = new Filesystem();
-            $fs->ensureDirectoryExists($this->checkoutDir);
-
-            if (!is_writable(dirname($this->checkoutDir))) {
-                throw new \RuntimeException('Can not clone '.$this->url.' to access package information. The "'.$this->checkoutDir.'" directory is not writable by the current user.');
-            }
-
-            // Ensure we are allowed to use this URL by config
-            $this->config->prohibitUrlByConfig($this->url, $this->io);
-
-            // update the repo if it is a valid fossil repository
-            if (is_file($this->repoFile) && is_dir($this->checkoutDir) && 0 === $this->process->execute('fossil info', $output, $this->checkoutDir)) {
-                if (0 !== $this->process->execute('fossil pull', $output, $this->checkoutDir)) {
-                    $this->io->writeError('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$this->process->getErrorOutput().')</error>');
-                }
-            } else {
-                // clean up directory and do a fresh clone into it
-                $fs->removeDirectory($this->checkoutDir);
-                $fs->remove($this->repoFile);
-
-                $fs->ensureDirectoryExists($this->checkoutDir);
-
-                if (0 !== $this->process->execute(sprintf('fossil clone %s %s', ProcessExecutor::escape($this->url), ProcessExecutor::escape($this->repoFile)), $output)) {
-                    $output = $this->process->getErrorOutput();
-
-                    if (0 !== $this->process->execute('fossil version', $ignoredOutput)) {
-                        throw new \RuntimeException('Failed to clone '.$this->url.', fossil was not found, check that it is installed and in your PATH env.' . "\n\n" . $this->process->getErrorOutput());
-                    }
-
-                    throw new \RuntimeException('Failed to clone '.$this->url.' to repository ' . $this->repoFile . "\n\n" .$output);
-                }
-
-                if (0 !== $this->process->execute(sprintf('fossil open %s', ProcessExecutor::escape($this->repoFile)), $output, $this->checkoutDir)) {
-                    $output = $this->process->getErrorOutput();
-
-                    throw new \RuntimeException('Failed to open repository '.$this->repoFile.' in ' . $this->checkoutDir . "\n\n" .$output);
-                }
-            }
+            $localName = preg_replace('{[^a-z0-9]}i', '-', $this->url);
+            $this->repoFile = $this->config->get('cache-repo-dir') . '/' . $localName . '.fossil';
+            $this->checkoutDir = $this->config->get('cache-vcs-dir') . '/' . $localName . '/';
         }
 
+        $this->updateLocalRepo();
+
         $this->getTags();
         $this->getBranches();
     }
 
+    /**
+     * Check that fossil can be invoked via command line.
+     */
+    protected function checkFossil()
+    {
+        if (0 !== $this->process->execute('fossil version', $ignoredOutput)) {
+            throw new \RuntimeException("fossil was not found, check that it is installed and in your PATH env.\n\n" . $this->process->getErrorOutput());
+        }
+    }
+
+    /**
+     * Clone or update existing local fossil repository.
+     */
+    protected function updateLocalRepo()
+    {
+        $fs = new Filesystem();
+        $fs->ensureDirectoryExists($this->checkoutDir);
+
+        if (!is_writable(dirname($this->checkoutDir))) {
+            throw new \RuntimeException('Can not clone '.$this->url.' to access package information. The "'.$this->checkoutDir.'" directory is not writable by the current user.');
+        }
+
+        // update the repo if it is a valid fossil repository
+        if (is_file($this->repoFile) && is_dir($this->checkoutDir) && 0 === $this->process->execute('fossil info', $output, $this->checkoutDir)) {
+            if (0 !== $this->process->execute('fossil pull', $output, $this->checkoutDir)) {
+                $this->io->writeError('<error>Failed to update '.$this->url.', package information from this repository may be outdated ('.$this->process->getErrorOutput().')</error>');
+            }
+        } else {
+            // clean up directory and do a fresh clone into it
+            $fs->removeDirectory($this->checkoutDir);
+            $fs->remove($this->repoFile);
+
+            $fs->ensureDirectoryExists($this->checkoutDir);
+
+            if (0 !== $this->process->execute(sprintf('fossil clone %s %s', ProcessExecutor::escape($this->url), ProcessExecutor::escape($this->repoFile)), $output)) {
+                $output = $this->process->getErrorOutput();
+
+                throw new \RuntimeException('Failed to clone '.$this->url.' to repository ' . $this->repoFile . "\n\n" .$output);
+            }
+
+            if (0 !== $this->process->execute(sprintf('fossil open %s', ProcessExecutor::escape($this->repoFile)), $output, $this->checkoutDir)) {
+                $output = $this->process->getErrorOutput();
+
+                throw new \RuntimeException('Failed to open repository '.$this->repoFile.' in ' . $this->checkoutDir . "\n\n" .$output);
+            }
+        }
+    }
+
     /**
      * {@inheritDoc}
      */