diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2153254a6..901bd1dc6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 1. [](#bugfix)
     * Fixed `Page::untranslatedLanguages()` not being symmetrical to `Page::translatedLanguages()`
     * Fixed `Flex Pages` not calling `onPageProcessed` event when cached
+    * Fixed phpstan issues in Framework up to level 6
 
 # v1.7.0-beta.10
 ## 10/03/2019
diff --git a/system/src/Grav/Framework/Cache/Adapter/ChainCache.php b/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
index e1eea7b6d..b530b3e89 100644
--- a/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/ChainCache.php
@@ -130,6 +130,10 @@ class ChainCache extends AbstractCache
     public function doGetMultiple($keys, $miss)
     {
         $list = [];
+        /**
+         * @var int $i
+         * @var CacheInterface $cache
+         */
         foreach ($this->caches as $i => $cache) {
             $list[$i] = $cache->doGetMultiple($keys, $miss);
 
@@ -140,8 +144,12 @@ class ChainCache extends AbstractCache
             }
         }
 
-        $values = [];
         // Update all the previous caches with missing values.
+        $values = [];
+        /**
+         * @var int $i
+         * @var CacheInterface $cache
+         */
         foreach (array_reverse($list) as $i => $items) {
             $values += $items;
             if ($i && $values) {
diff --git a/system/src/Grav/Framework/Cache/Adapter/FileCache.php b/system/src/Grav/Framework/Cache/Adapter/FileCache.php
index a5a60fa5f..3d3a2ec1d 100644
--- a/system/src/Grav/Framework/Cache/Adapter/FileCache.php
+++ b/system/src/Grav/Framework/Cache/Adapter/FileCache.php
@@ -51,12 +51,12 @@ class FileCache extends AbstractCache
             fclose($h);
             @unlink($file);
         } else {
-            $i = rawurldecode(rtrim(fgets($h)));
-            $value = stream_get_contents($h);
+            $i = rawurldecode(rtrim((string)fgets($h)));
+            $value = stream_get_contents($h) ?: '';
             fclose($h);
 
             if ($i === $key) {
-                return unserialize($value);
+                return unserialize($value, ['allowed_classes' => true]);
             }
         }
 
diff --git a/system/src/Grav/Framework/Collection/AbstractFileCollection.php b/system/src/Grav/Framework/Collection/AbstractFileCollection.php
index 61b3dfeb3..41471012f 100644
--- a/system/src/Grav/Framework/Collection/AbstractFileCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractFileCollection.php
@@ -94,6 +94,10 @@ class AbstractFileCollection extends AbstractLazyCollection implements FileColle
 
         if ($orderings = $criteria->getOrderings()) {
             $next = null;
+            /**
+             * @var string $field
+             * @var string $ordering
+             */
             foreach (array_reverse($orderings) as $field => $ordering) {
                 $next = ClosureExpressionVisitor::sortByField($field, $ordering === Criteria::DESC ? -1 : 1, $next);
             }
diff --git a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
index 7bb5af620..059dd9d48 100644
--- a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
@@ -44,7 +44,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     public function first()
     {
         $value = reset($this->entries);
-        $key = key($this->entries);
+        $key = (string)key($this->entries);
 
         return $this->loadElement($key, $value);
     }
@@ -55,7 +55,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     public function last()
     {
         $value = end($this->entries);
-        $key = key($this->entries);
+        $key = (string)key($this->entries);
 
         return $this->loadElement($key, $value);
     }
@@ -65,7 +65,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
      */
     public function key()
     {
-        return key($this->entries);
+        return (string)key($this->entries);
     }
 
     /**
@@ -74,7 +74,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     public function next()
     {
         $value = next($this->entries);
-        $key = key($this->entries);
+        $key = (string)key($this->entries);
 
         return $this->loadElement($key, $value);
     }
@@ -85,7 +85,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     public function current()
     {
         $value = current($this->entries);
-        $key = key($this->entries);
+        $key = (string)key($this->entries);
 
         return $this->loadElement($key, $value);
     }
@@ -102,7 +102,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
         $value = $this->entries[$key];
         unset($this->entries[$key]);
 
-        return $this->loadElement($key, $value);
+        return $this->loadElement((string)$key, $value);
     }
 
     /**
@@ -210,7 +210,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
             return null;
         }
 
-        return $this->loadElement($key, $this->entries[$key]);
+        return $this->loadElement((string)$key, $this->entries[$key]);
     }
 
     /**
diff --git a/system/src/Grav/Framework/Collection/CollectionInterface.php b/system/src/Grav/Framework/Collection/CollectionInterface.php
index 9239d4ace..4d0b59120 100644
--- a/system/src/Grav/Framework/Collection/CollectionInterface.php
+++ b/system/src/Grav/Framework/Collection/CollectionInterface.php
@@ -21,14 +21,14 @@ interface CollectionInterface extends Collection, \JsonSerializable
     /**
      * Reverse the order of the items.
      *
-     * @return static
+     * @return static|CollectionInterface
      */
     public function reverse();
 
     /**
      * Shuffle items.
      *
-     * @return static
+     * @return static|CollectionInterface
      */
     public function shuffle();
 
@@ -46,7 +46,7 @@ interface CollectionInterface extends Collection, \JsonSerializable
      * Collection is returned in the order of $keys given to the function.
      *
      * @param array $keys
-     * @return static
+     * @return static|CollectionInterface
      */
     public function select(array $keys);
 
@@ -54,7 +54,7 @@ interface CollectionInterface extends Collection, \JsonSerializable
      * Un-select items from collection.
      *
      * @param array $keys
-     * @return static
+     * @return static|CollectionInterface
      */
     public function unselect(array $keys);
 }
diff --git a/system/src/Grav/Framework/File/AbstractFile.php b/system/src/Grav/Framework/File/AbstractFile.php
index 0411701d3..9f34ab938 100644
--- a/system/src/Grav/Framework/File/AbstractFile.php
+++ b/system/src/Grav/Framework/File/AbstractFile.php
@@ -158,7 +158,7 @@ class AbstractFile implements FileInterface
      */
     public function getCreationTime(): int
     {
-        return is_file($this->filepath) ? filectime($this->filepath) : time();
+        return is_file($this->filepath) ? (int)filectime($this->filepath) : time();
     }
 
     /**
@@ -167,7 +167,7 @@ class AbstractFile implements FileInterface
      */
     public function getModificationTime(): int
     {
-        return is_file($this->filepath) ? filemtime($this->filepath) : time();
+        return is_file($this->filepath) ? (int)filemtime($this->filepath) : time();
     }
 
     /**
@@ -180,7 +180,7 @@ class AbstractFile implements FileInterface
             if (!$this->mkdir($this->getPath())) {
                 throw new \RuntimeException('Creating directory failed for ' . $this->filepath);
             }
-            $this->handle = @fopen($this->filepath, 'cb+');
+            $this->handle = @fopen($this->filepath, 'cb+') ?: null;
             if (!$this->handle) {
                 $error = error_get_last();
 
@@ -382,6 +382,7 @@ class AbstractFile implements FileInterface
 
     protected function setPathInfo(): void
     {
+        /** @var array $pathInfo */
         $pathInfo = $this->filesystem->pathinfo($this->filepath);
 
         $this->filename = $pathInfo['filename'] ?? null;
diff --git a/system/src/Grav/Framework/File/DataFile.php b/system/src/Grav/Framework/File/DataFile.php
index 491487132..3a0e79270 100644
--- a/system/src/Grav/Framework/File/DataFile.php
+++ b/system/src/Grav/Framework/File/DataFile.php
@@ -40,7 +40,11 @@ class DataFile extends AbstractFile
         $raw = parent::load();
 
         try {
-            return $raw !== false ? $this->formatter->decode($raw) : false;
+            if (!is_string($raw)) {
+                throw new RuntimeException('Bad Data');
+            }
+
+            return $this->formatter->decode($raw);
         } catch (RuntimeException $e) {
             throw new RuntimeException(sprintf("Failed to load file '%s': %s", $this->getFilePath(), $e->getMessage()), $e->getCode(), $e);
         }
diff --git a/system/src/Grav/Framework/File/Formatter/AbstractFormatter.php b/system/src/Grav/Framework/File/Formatter/AbstractFormatter.php
index 549ff6ff3..bd8e0c025 100644
--- a/system/src/Grav/Framework/File/Formatter/AbstractFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/AbstractFormatter.php
@@ -57,7 +57,7 @@ abstract class AbstractFormatter implements FileFormatterInterface
         $extensions = $this->getSupportedFileExtensions();
 
         // Call fails on bad configuration.
-        return reset($extensions);
+        return reset($extensions) ?: '';
     }
 
     /**
diff --git a/system/src/Grav/Framework/File/Formatter/CsvFormatter.php b/system/src/Grav/Framework/File/Formatter/CsvFormatter.php
index 6c1c3b4f4..667cdad1e 100644
--- a/system/src/Grav/Framework/File/Formatter/CsvFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/CsvFormatter.php
@@ -91,7 +91,7 @@ class CsvFormatter extends AbstractFormatter
                     $csv_line = str_getcsv($line, $delimiter);
 
                     if ($null_replace) {
-                        array_walk($csv_line, function(&$el) use ($null_replace) {
+                        array_walk($csv_line, static function(&$el) use ($null_replace) {
                            $el = str_replace($null_replace, null, $el);
                         });
                     }
@@ -100,7 +100,7 @@ class CsvFormatter extends AbstractFormatter
                 }
             }
         } catch (\Exception $e) {
-            throw new \Exception('Badly formatted CSV line: ' . $line);
+            throw new \RuntimeException('Badly formatted CSV line: ' . $line);
         }
 
         return $list;
diff --git a/system/src/Grav/Framework/File/Formatter/JsonFormatter.php b/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
index 1ae16ae29..5411bbc47 100644
--- a/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/JsonFormatter.php
@@ -80,7 +80,7 @@ class JsonFormatter extends AbstractFormatter
             throw new \RuntimeException('Encoding JSON failed: ' . json_last_error_msg());
         }
 
-        return $encoded;
+        return $encoded ?: '';
     }
 
     /**
diff --git a/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php b/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
index 73ed8122f..55f46cfec 100644
--- a/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
+++ b/system/src/Grav/Framework/File/Formatter/SerializeFormatter.php
@@ -34,7 +34,7 @@ class SerializeFormatter extends AbstractFormatter
      *
      * By default only allow stdClass class.
      *
-     * @return array|bool
+     * @return array
      */
     public function getOptions()
     {
@@ -56,7 +56,8 @@ class SerializeFormatter extends AbstractFormatter
      */
     public function decode($data)
     {
-        $decoded = @unserialize($data, $this->getOptions());
+        $classes = $this->getOptions()['allowed_classes'] ?? false;
+        $decoded = @unserialize($data, ['allowed_classes' => $classes]);
 
         if ($decoded === false && $data !== serialize(false)) {
             throw new \RuntimeException('Decoding serialized data failed');
@@ -86,4 +87,4 @@ class SerializeFormatter extends AbstractFormatter
 
         return $data;
     }
-}
\ No newline at end of file
+}
diff --git a/system/src/Grav/Framework/Filesystem/Filesystem.php b/system/src/Grav/Framework/Filesystem/Filesystem.php
index 473a2eca5..9cd206df4 100644
--- a/system/src/Grav/Framework/Filesystem/Filesystem.php
+++ b/system/src/Grav/Framework/Filesystem/Filesystem.php
@@ -184,11 +184,15 @@ class Filesystem implements FilesystemInterface
      * @param string $path
      * @param int|null $options
      *
-     * @return array
+     * @return array|string
      */
     protected function pathinfoInternal(?string $scheme, string $path, int $options = null)
     {
-        $info = $options ? \pathinfo($path, $options) : \pathinfo($path);
+        if ($options) {
+            return \pathinfo($path, $options);
+        }
+
+        $info = \pathinfo($path);
 
         if (null !== $scheme) {
             $info['scheme'] = $scheme;
diff --git a/system/src/Grav/Framework/Flex/FlexCollection.php b/system/src/Grav/Framework/Flex/FlexCollection.php
index 63528d1ed..55fcb8825 100644
--- a/system/src/Grav/Framework/Flex/FlexCollection.php
+++ b/system/src/Grav/Framework/Flex/FlexCollection.php
@@ -25,6 +25,7 @@ use Psr\SimpleCache\InvalidArgumentException;
 use RocketTheme\Toolbox\Event\Event;
 use Twig\Error\LoaderError;
 use Twig\Error\SyntaxError;
+use Twig\Template;
 use Twig\TemplateWrapper;
 
 /**
@@ -201,7 +202,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
      */
     public function getCacheKey(): string
     {
-        return $this->getTypePrefix() . $this->getFlexType() . '.' . sha1(json_encode($this->call('getKey')));
+        return $this->getTypePrefix() . $this->getFlexType() . '.' . sha1((string)json_encode($this->call('getKey')));
     }
 
     /**
@@ -219,7 +220,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
             $list[$key] = $object->getCacheChecksum();
         }
 
-        return sha1(json_encode($list));
+        return sha1((string)json_encode($list));
     }
 
     /**
@@ -331,7 +332,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
         }
 
         try {
-            $data = $cache ? $cache->get($key) : null;
+            $data = $cache && $key ? $cache->get($key) : null;
 
             $block = $data ? HtmlBlock::fromArray($data) : null;
         } catch (InvalidArgumentException $e) {
@@ -371,7 +372,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
             $block->setContent($output);
 
             try {
-                $cache && $block->isCached() && $cache->set($key, $block->toArray());
+                $cache && $key && $block->isCached() && $cache->set($key, $block->toArray());
             } catch (InvalidArgumentException $e) {
                 $debugger->addException($e);
             }
@@ -522,7 +523,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
 
     /**
      * @param string $layout
-     * @return TemplateWrapper
+     * @return Template|TemplateWrapper
      * @throws LoaderError
      * @throws SyntaxError
      */
diff --git a/system/src/Grav/Framework/Flex/FlexDirectory.php b/system/src/Grav/Framework/Flex/FlexDirectory.php
index 8d7487fe8..557f82d32 100644
--- a/system/src/Grav/Framework/Flex/FlexDirectory.php
+++ b/system/src/Grav/Framework/Flex/FlexDirectory.php
@@ -221,6 +221,7 @@ class FlexDirectory implements FlexAuthorizeInterface
         $index = $index->withKeyField($keyField);
 
         if (null !== $keys) {
+            /** @var FlexCollectionInterface $index */
             $index = $index->select($keys);
         }
 
@@ -694,17 +695,9 @@ class FlexDirectory implements FlexAuthorizeInterface
             $params = [$object instanceof PageInterface && $object->modular() ? 'modular' : 'standard'];
         }
 
-        [$o, $f] = explode('::', $function, 2);
-
         $data = null;
-        if (!$f) {
-            if (\function_exists($o)) {
-                $data = \call_user_func_array($o, $params);
-            }
-        } else {
-            if (method_exists($o, $f)) {
-                $data = \call_user_func_array([$o, $f], $params);
-            }
+        if (\is_callable($function)) {
+            $data = \call_user_func_array($function, $params);
         }
 
         // If function returns a value,
diff --git a/system/src/Grav/Framework/Flex/FlexIndex.php b/system/src/Grav/Framework/Flex/FlexIndex.php
index 1cb088a40..9adcb5087 100644
--- a/system/src/Grav/Framework/Flex/FlexIndex.php
+++ b/system/src/Grav/Framework/Flex/FlexIndex.php
@@ -185,7 +185,7 @@ class FlexIndex extends ObjectIndex implements FlexCollectionInterface, FlexInde
             $list[$key] = $value['checksum'] ?? $value['storage_timestamp'];
         }
 
-        return sha1(json_encode($list));
+        return sha1((string)json_encode($list));
     }
 
     /**
diff --git a/system/src/Grav/Framework/Flex/Pages/FlexPageCollection.php b/system/src/Grav/Framework/Flex/Pages/FlexPageCollection.php
index 1b7a65277..1267bebc0 100644
--- a/system/src/Grav/Framework/Flex/Pages/FlexPageCollection.php
+++ b/system/src/Grav/Framework/Flex/Pages/FlexPageCollection.php
@@ -11,7 +11,6 @@ declare(strict_types=1);
 
 namespace Grav\Framework\Flex\Pages;
 
-use Grav\Common\Page\Interfaces\PageCollectionInterface;
 use Grav\Common\Page\Interfaces\PageInterface;
 use Grav\Framework\Flex\FlexCollection;
 use Grav\Framework\Flex\Interfaces\FlexCollectionInterface;
@@ -116,7 +115,7 @@ class FlexPageCollection extends FlexCollection
      * @param  string  $path
      * @param  int $direction either -1 or +1
      *
-     * @return PageInterface|PageCollectionInterface|null    The sibling item.
+     * @return PageInterface|null    The sibling item.
      */
     public function adjacentSibling($path, $direction = 1)
     {
diff --git a/system/src/Grav/Framework/Flex/Storage/SimpleStorage.php b/system/src/Grav/Framework/Flex/Storage/SimpleStorage.php
index 0b2815347..0beb2e7bf 100644
--- a/system/src/Grav/Framework/Flex/Storage/SimpleStorage.php
+++ b/system/src/Grav/Framework/Flex/Storage/SimpleStorage.php
@@ -243,7 +243,7 @@ class SimpleStorage extends AbstractFilesystemStorage
             $this->save();
 
             foreach ($list as $key => $row) {
-                $list[$key]['__META'] = $this->getObjectMeta($key, true);
+                $list[$key]['__META'] = $this->getObjectMeta((string)$key, true);
             }
         }
 
@@ -347,7 +347,7 @@ class SimpleStorage extends AbstractFilesystemStorage
             }
             $file = $this->getFile($path);
             $file->save($this->data);
-            $this->modified = $file->modified();
+            $this->modified = (int)$file->modified(); // cast false to 0
             $file->free();
         } catch (\RuntimeException $e) {
             throw new \RuntimeException(sprintf('Flex save(): %s', $e->getMessage()));
@@ -378,7 +378,7 @@ class SimpleStorage extends AbstractFilesystemStorage
         }
 
         $file = $this->getFile($path);
-        $this->modified = $file->modified();
+        $this->modified = (int)$file->modified(); // cast false to 0
         $this->data = (array) $file->content();
 
         $list = [];