diff --git a/src/Composer/DependencyResolver/PoolBuilder.php b/src/Composer/DependencyResolver/PoolBuilder.php
index 8ca7050fd9ff..69769ca7f189 100644
--- a/src/Composer/DependencyResolver/PoolBuilder.php
+++ b/src/Composer/DependencyResolver/PoolBuilder.php
@@ -287,6 +287,8 @@ public function buildPool(array $repositories, Request $request)
         $this->skippedLoad = array();
         $this->indexCounter = 0;
 
+        $this->io->debug('Built pool.');
+
         $pool = $this->runOptimizer($request, $pool);
 
         Intervals::clear();
@@ -690,6 +692,9 @@ private function runOptimizer(Request $request, Pool $pool)
             return $pool;
         }
 
+        $this->io->debug('Running pool optimizer.');
+
+        $before = microtime(true);
         $total = \count($pool->getPackages());
 
         $pool = $this->poolOptimizer->optimize($request, $pool);
@@ -700,6 +705,7 @@ private function runOptimizer(Request $request, Pool $pool)
             return $pool;
         }
 
+        $this->io->write(sprintf('Pool optimizer completed in %.3f seconds', microtime(true) - $before), true, IOInterface::VERY_VERBOSE);
         $this->io->write(sprintf(
             '<info>Found %s package versions referenced in your dependency graph. %s (%d%%) were optimized away.</info>',
             number_format($total),
diff --git a/src/Composer/DependencyResolver/PoolOptimizer.php b/src/Composer/DependencyResolver/PoolOptimizer.php
index 7e1e32fdcb02..6cbd670f1cbc 100644
--- a/src/Composer/DependencyResolver/PoolOptimizer.php
+++ b/src/Composer/DependencyResolver/PoolOptimizer.php
@@ -339,6 +339,11 @@ private function markPackageForRemoval($id)
      */
     private function keepPackage(BasePackage $package, $identicalDefinitionsPerPackage, $packageIdenticalDefinitionLookup)
     {
+        // Already marked to keep
+        if (!isset($this->packagesToRemove[$package->id])) {
+            return;
+        }
+
         unset($this->packagesToRemove[$package->id]);
 
         if ($package instanceof AliasPackage) {