diff --git a/.gitignore b/.gitignore
index 3452648..5186b79 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 /vendor/
 composer.lock
 .php_cs.cache
+.phpunit.result.cache
diff --git a/Makefile b/Makefile
index 1196ddf..9caad7d 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,7 @@ test:
 	vendor/bin/phpunit --testdox --colors=always --group=functional
 
 .PHONY: qa
-qa: php-cs-fixer-ci
+qa: php-cs-fixer-ci phpstan
 
 .PHONY: php-cs-fixer
 php-cs-fixer:
@@ -20,6 +20,10 @@ php-cs-fixer:
 php-cs-fixer-ci:
 	vendor/bin/php-cs-fixer fix --dry-run --no-interaction --allow-risky=yes --diff --verbose
 
+PHONY: phpstan
+phpstan:
+	vendor/bin/phpstan analyse --level=max src/
+
 .PHONY: changelog
 changelog:
 	git log $$(git describe --abbrev=0 --tags)...HEAD --no-merges --pretty=format:"* [%h](http://github.com/${TRAVIS_REPO_SLUG}/commit/%H) %s (%cN)"
diff --git a/composer.json b/composer.json
index 8b9d26b..f9a6026 100644
--- a/composer.json
+++ b/composer.json
@@ -35,7 +35,8 @@
     ],
     "require-dev": {
         "phpunit/phpunit": "^8.0",
-        "broadway/coding-standard": "^1.0"
+        "broadway/coding-standard": "^1.0",
+        "phpstan/phpstan": "@stable"
     },
     "autoload": {
         "psr-4": {
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..9d52fd9
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,2 @@
+parameters:
+    checkMissingIterableValueType: false
diff --git a/src/ElasticSearchRepository.php b/src/ElasticSearchRepository.php
index 202069d..15553fc 100644
--- a/src/ElasticSearchRepository.php
+++ b/src/ElasticSearchRepository.php
@@ -25,10 +25,19 @@
  */
 class ElasticSearchRepository implements Repository
 {
+    /** @var Client */
     private $client;
+
+    /** @var Serializer */
     private $serializer;
+
+    /** @var string */
     private $index;
+
+    /** @var string */
     private $class;
+
+    /** @var string[] */
     private $notAnalyzedFields;
 
     public function __construct(
@@ -121,7 +130,7 @@ public function remove($id): void
         }
     }
 
-    private function searchAndDeserializeHits(array $query)
+    private function searchAndDeserializeHits(array $query): array
     {
         try {
             $result = $this->client->search($query);
@@ -153,7 +162,7 @@ protected function search(array $query, array $facets = [], int $size = 500): ar
         }
     }
 
-    protected function query(array $query)
+    protected function query(array $query): array
     {
         return $this->searchAndDeserializeHits(
             [
@@ -183,7 +192,7 @@ private function buildFindAllQuery(): array
         ];
     }
 
-    private function deserializeHit(array $hit)
+    private function deserializeHit(array $hit): Identifiable
     {
         return $this->serializer->deserialize(
             [
@@ -193,12 +202,12 @@ private function deserializeHit(array $hit)
         );
     }
 
-    private function deserializeHits(array $hits)
+    private function deserializeHits(array $hits): array
     {
         return array_map([$this, 'deserializeHit'], $hits);
     }
 
-    private function buildFilter(array $filter)
+    private function buildFilter(array $filter): array
     {
         $retval = [];
 
@@ -247,8 +256,6 @@ public function createIndex(): bool
 
     /**
      * Deletes the index for this repository's ReadModel.
-     *
-     * @return True, if the index was successfully deleted
      */
     public function deleteIndex(): bool
     {
diff --git a/src/ElasticSearchRepositoryFactory.php b/src/ElasticSearchRepositoryFactory.php
index a26bb72..d78e486 100644
--- a/src/ElasticSearchRepositoryFactory.php
+++ b/src/ElasticSearchRepositoryFactory.php
@@ -23,7 +23,10 @@
  */
 class ElasticSearchRepositoryFactory implements RepositoryFactory
 {
+    /** @var Client */
     private $client;
+
+    /** @var Serializer */
     private $serializer;
 
     public function __construct(Client $client, Serializer $serializer)