diff --git a/.travis.yml b/.travis.yml
index 667d3f2d0..b6b914adf 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -14,13 +14,16 @@ env:
 before_script:
   - if [[ $TRAVIS_PHP_VERSION = '7.1' && $DB = 'sqlite' && "$DEPENDENCIES" != "low" ]]; then PHPUNIT_FLAGS="--coverage-clover ./build/logs/clover.xml"; else PHPUNIT_FLAGS=""; fi
   - if [[ "$PHPUNIT_FLAGS" == "" ]]; then phpenv config-rm xdebug.ini; fi
+  - if [[ $PHPSTAN = 1 ]]; then echo "extension=redis.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini; fi
   - composer self-update
   - composer install --prefer-source
   - if [ "$DEPENDENCIES" != "low" ]; then composer update; fi;
   - if [ "$DEPENDENCIES" == "low" ]; then composer update --prefer-lowest; fi;
+  - if [[ $PHPSTAN = 1 ]]; then composer require --dev --prefer-stable phpstan/phpstan:^0.7 symfony/console:^3.0; fi
   - if [[ $DB == "mysql" || $DB == "mariadb" ]]; then mysql -e "CREATE SCHEMA doctrine_tests; GRANT ALL PRIVILEGES ON doctrine_tests.* to travis@'%'"; fi;
 
 script:
+  - if [[ $PHPSTAN = 1 ]]; then vendor/bin/phpstan analyse -l 0 -c phpstan.neon lib; fi
   - ENABLE_SECOND_LEVEL_CACHE=0 ./vendor/bin/phpunit -v -c tests/travis/$DB.travis.xml $PHPUNIT_FLAGS
   - ENABLE_SECOND_LEVEL_CACHE=1 ./vendor/bin/phpunit -v -c tests/travis/$DB.travis.xml --exclude-group performance,non-cacheable,locking_functional
 
@@ -39,6 +42,10 @@ matrix:
       env:
         - DB=sqlite
         - DEPENDENCIES='low'
+    - php: 7.1
+      env:
+        - DB=pgsql
+        - PHPSTAN=1
 
   allow_failures:
     - php: nightly
diff --git a/lib/Doctrine/ORM/PersistentCollection.php b/lib/Doctrine/ORM/PersistentCollection.php
index 11205df04..a5024b8d9 100644
--- a/lib/Doctrine/ORM/PersistentCollection.php
+++ b/lib/Doctrine/ORM/PersistentCollection.php
@@ -514,10 +514,11 @@ final class PersistentCollection extends AbstractLazyCollection implements Selec
     public function offsetSet($offset, $value)
     {
         if ( ! isset($offset)) {
-            return $this->add($value);
+            $this->add($value);
+            return;
         }
 
-        return $this->set($offset, $value);
+        $this->set($offset, $value);
     }
 
     /**
diff --git a/lib/Doctrine/ORM/Query/ResultSetMapping.php b/lib/Doctrine/ORM/Query/ResultSetMapping.php
index 5c4550980..efffa674c 100644
--- a/lib/Doctrine/ORM/Query/ResultSetMapping.php
+++ b/lib/Doctrine/ORM/Query/ResultSetMapping.php
@@ -451,7 +451,7 @@ class ResultSetMapping
     /**
      * @param string $alias
      *
-     * @return AssociationMapping
+     * @return string
      */
     public function getRelation($alias)
     {
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 000000000..cc74bf06e
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,4 @@
+parameters:
+    ignoreErrors:
+        # Memcache does not exist on PHP 7
+        - '#Instantiated class Memcache not found#'