diff --git a/system/src/Grav/Common/Assets/BaseAsset.php b/system/src/Grav/Common/Assets/BaseAsset.php
index a115ce9ec..a80d9c6d9 100644
--- a/system/src/Grav/Common/Assets/BaseAsset.php
+++ b/system/src/Grav/Common/Assets/BaseAsset.php
@@ -248,6 +248,7 @@ abstract class BaseAsset extends PropertyObject
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return ['type' => $this->getType(), 'elements' => $this->getElements()];
diff --git a/system/src/Grav/Common/Data/Data.php b/system/src/Grav/Common/Data/Data.php
index 4de437dcb..60ee9534d 100644
--- a/system/src/Grav/Common/Data/Data.php
+++ b/system/src/Grav/Common/Data/Data.php
@@ -335,6 +335,7 @@ class Data implements DataInterface, ArrayAccess, \Countable, JsonSerializable,
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->items;
diff --git a/system/src/Grav/Common/Flex/Types/Users/Traits/UserObjectLegacyTrait.php b/system/src/Grav/Common/Flex/Types/Users/Traits/UserObjectLegacyTrait.php
index b0fc0c4ca..e2f87f716 100644
--- a/system/src/Grav/Common/Flex/Types/Users/Traits/UserObjectLegacyTrait.php
+++ b/system/src/Grav/Common/Flex/Types/Users/Traits/UserObjectLegacyTrait.php
@@ -84,6 +84,7 @@ trait UserObjectLegacyTrait
      * @return int
      * @deprecated 1.6 Method makes no sense for user account.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         user_error(__CLASS__ . '::' . __FUNCTION__ . '() is deprecated since Grav 1.6', E_USER_DEPRECATED);
diff --git a/system/src/Grav/Common/GPM/Remote/Package.php b/system/src/Grav/Common/GPM/Remote/Package.php
index c37d6a00d..1e838053d 100644
--- a/system/src/Grav/Common/GPM/Remote/Package.php
+++ b/system/src/Grav/Common/GPM/Remote/Package.php
@@ -32,6 +32,7 @@ class Package extends BasePackage implements \JsonSerializable
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->data->toArray();
diff --git a/system/src/Grav/Common/Getters.php b/system/src/Grav/Common/Getters.php
index 916d5249a..10f4fdb7a 100644
--- a/system/src/Grav/Common/Getters.php
+++ b/system/src/Grav/Common/Getters.php
@@ -129,6 +129,7 @@ abstract class Getters implements ArrayAccess, Countable
     /**
      * @return int
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         if ($this->gettersVariable) {
diff --git a/system/src/Grav/Common/Page/Header.php b/system/src/Grav/Common/Page/Header.php
index 71c7b16c3..0ab9af407 100644
--- a/system/src/Grav/Common/Page/Header.php
+++ b/system/src/Grav/Common/Page/Header.php
@@ -30,6 +30,7 @@ class Header implements ArrayAccess, ExportInterface, JsonSerializable
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->toArray();
diff --git a/system/src/Grav/Common/Page/Medium/Link.php b/system/src/Grav/Common/Page/Medium/Link.php
index d57687573..e3c98a853 100644
--- a/system/src/Grav/Common/Page/Medium/Link.php
+++ b/system/src/Grav/Common/Page/Medium/Link.php
@@ -28,7 +28,7 @@ class Link implements RenderableInterface, MediaLinkInterface
 
     /** @var array */
     protected $attributes = [];
-    /** @var MediaObjectInterface */
+    /** @var MediaObjectInterface|MediaLinkInterface */
     protected $source;
 
     /**
diff --git a/system/src/Grav/Common/Page/Page.php b/system/src/Grav/Common/Page/Page.php
index 9e68a44f8..f67212aeb 100644
--- a/system/src/Grav/Common/Page/Page.php
+++ b/system/src/Grav/Common/Page/Page.php
@@ -84,7 +84,7 @@ class Page implements PageInterface
     protected $unpublish_date;
     /** @var string */
     protected $slug;
-    /** @var string */
+    /** @var string|null */
     protected $route;
     /** @var string|null */
     protected $raw_route;
diff --git a/system/src/Grav/Common/User/DataUser/User.php b/system/src/Grav/Common/User/DataUser/User.php
index 8fcdbbbd6..0b8a53b9e 100644
--- a/system/src/Grav/Common/User/DataUser/User.php
+++ b/system/src/Grav/Common/User/DataUser/User.php
@@ -295,6 +295,7 @@ class User extends Data implements UserInterface
      * @return int
      * @deprecated 1.6 Method makes no sense for user account.
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         user_error(__CLASS__ . '::' . __FUNCTION__ . '() is deprecated since Grav 1.6', E_USER_DEPRECATED);
diff --git a/system/src/Grav/Framework/Acl/Permissions.php b/system/src/Grav/Framework/Acl/Permissions.php
index 037571675..8372f725d 100644
--- a/system/src/Grav/Framework/Acl/Permissions.php
+++ b/system/src/Grav/Framework/Acl/Permissions.php
@@ -206,6 +206,7 @@ class Permissions implements \ArrayAccess, \Countable, \IteratorAggregate
     /**
      * @return ArrayIterator|Traversable
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new ArrayIterator($this->actions);
diff --git a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
index 4974a3acf..c2f57f2c1 100644
--- a/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractIndexCollection.php
@@ -257,6 +257,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
     /**
      * {@inheritDoc}
      */
+    #[\ReturnTypeWillChange]
     public function count()
     {
         return count($this->entries);
@@ -301,6 +302,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
      *
      * {@inheritDoc}
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new ArrayIterator($this->loadElements());
@@ -468,6 +470,7 @@ abstract class AbstractIndexCollection implements CollectionInterface
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->loadCollection()->jsonSerialize();
diff --git a/system/src/Grav/Framework/Collection/AbstractLazyCollection.php b/system/src/Grav/Framework/Collection/AbstractLazyCollection.php
index 9afaab131..d7e6f3191 100644
--- a/system/src/Grav/Framework/Collection/AbstractLazyCollection.php
+++ b/system/src/Grav/Framework/Collection/AbstractLazyCollection.php
@@ -78,6 +78,7 @@ abstract class AbstractLazyCollection extends BaseAbstractLazyCollection impleme
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $this->initialize();
diff --git a/system/src/Grav/Framework/Collection/ArrayCollection.php b/system/src/Grav/Framework/Collection/ArrayCollection.php
index d76aa05dc..4a54b3cb9 100644
--- a/system/src/Grav/Framework/Collection/ArrayCollection.php
+++ b/system/src/Grav/Framework/Collection/ArrayCollection.php
@@ -97,6 +97,7 @@ class ArrayCollection extends BaseArrayCollection implements CollectionInterface
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->toArray();
diff --git a/system/src/Grav/Framework/Flex/FlexCollection.php b/system/src/Grav/Framework/Flex/FlexCollection.php
index c76c3061b..dfba12cb9 100644
--- a/system/src/Grav/Framework/Flex/FlexCollection.php
+++ b/system/src/Grav/Framework/Flex/FlexCollection.php
@@ -520,6 +520,7 @@ class FlexCollection extends ObjectCollection implements FlexCollectionInterface
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         $elements = [];
diff --git a/system/src/Grav/Framework/Flex/FlexObject.php b/system/src/Grav/Framework/Flex/FlexObject.php
index ac51b3461..41f825512 100644
--- a/system/src/Grav/Framework/Flex/FlexObject.php
+++ b/system/src/Grav/Framework/Flex/FlexObject.php
@@ -656,6 +656,7 @@ class FlexObject implements FlexObjectInterface, FlexAuthorizeInterface
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->getElements();
diff --git a/system/src/Grav/Framework/Form/FormFlashFile.php b/system/src/Grav/Framework/Form/FormFlashFile.php
index 51c318346..2db2bd9a2 100644
--- a/system/src/Grav/Framework/Form/FormFlashFile.php
+++ b/system/src/Grav/Framework/Form/FormFlashFile.php
@@ -176,6 +176,7 @@ class FormFlashFile implements UploadedFileInterface, JsonSerializable
     /**
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->upload;
diff --git a/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php b/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
index c4c470539..ba7c2d4ee 100644
--- a/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
+++ b/system/src/Grav/Framework/Object/Base/ObjectCollectionTrait.php
@@ -181,6 +181,7 @@ trait ObjectCollectionTrait
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->doSerialize();
diff --git a/system/src/Grav/Framework/Object/Base/ObjectTrait.php b/system/src/Grav/Framework/Object/Base/ObjectTrait.php
index d4e324b46..9b13328f9 100644
--- a/system/src/Grav/Framework/Object/Base/ObjectTrait.php
+++ b/system/src/Grav/Framework/Object/Base/ObjectTrait.php
@@ -172,6 +172,7 @@ trait ObjectTrait
      *
      * @return array
      */
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return $this->doSerialize();
diff --git a/system/src/Grav/Framework/Pagination/AbstractPagination.php b/system/src/Grav/Framework/Pagination/AbstractPagination.php
index 0be21ec3b..2e6f815f8 100644
--- a/system/src/Grav/Framework/Pagination/AbstractPagination.php
+++ b/system/src/Grav/Framework/Pagination/AbstractPagination.php
@@ -235,6 +235,7 @@ class AbstractPagination implements PaginationInterface
     /**
      * @return ArrayIterator
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         $this->loadItems();
diff --git a/system/src/Grav/Framework/Session/Session.php b/system/src/Grav/Framework/Session/Session.php
index 3feae5a2a..dc6ce8292 100644
--- a/system/src/Grav/Framework/Session/Session.php
+++ b/system/src/Grav/Framework/Session/Session.php
@@ -392,6 +392,7 @@ class Session implements SessionInterface
     /**
      * @inheritdoc
      */
+    #[\ReturnTypeWillChange]
     public function getIterator()
     {
         return new ArrayIterator($_SESSION);
diff --git a/system/src/Grav/Framework/Session/SessionInterface.php b/system/src/Grav/Framework/Session/SessionInterface.php
index 43ca40fd9..fcf5061fb 100644
--- a/system/src/Grav/Framework/Session/SessionInterface.php
+++ b/system/src/Grav/Framework/Session/SessionInterface.php
@@ -108,6 +108,7 @@ interface SessionInterface extends IteratorAggregate
      *
      * @return ArrayIterator Return an ArrayIterator of $_SESSION
      */
+    #[\ReturnTypeWillChange]
     public function getIterator();
 
     /**
diff --git a/tests/phpstan/phpstan.neon b/tests/phpstan/phpstan.neon
index aec8c4657..3c99f24c4 100644
--- a/tests/phpstan/phpstan.neon
+++ b/tests/phpstan/phpstan.neon
@@ -33,13 +33,9 @@ parameters:
     dynamicConstantNames:
         - GRAV_CLI
     ignoreErrors:
-        # New in phpstan 0.12, ignore them for now.
+        # New in phpstan 1, ignore them for now.
         - '#Unsafe usage of new static\(\)#'
         - '#Cannot instantiate interface Grav\\Framework\\#'
-        # TODO: phpstan bug #3875 (fixed, test if can be removed)
-        -
-            message: '#Unreachable statement - code above always terminates#'
-            path: '*/system/src/Grav/Common/Flex/Types/Pages/Storage/PageStorage.php'
 
         # FIXME: Bugs that need to be fixed
         # FIXME: PHP 7.3 bug workaround
@@ -84,12 +80,12 @@ parameters:
         -
             message: '#unknown class Grav\\Plugin\\Admin#'
             path: '*/system/src/Grav/Common/Flex/Pages/PageObject.php'
-        -
-            message: '#unknown class Grav\\Common\\Grav\\Plugin\\Form\\Forms#'
-            path: '*/system/src/Grav/Common/Session.php'
         -
             message: '#unknown class Grav\\Plugin\\Admin\\Admin#'
             path: '*/system/src/Grav/Common/Flex/Types/Pages/PageObject.php'
+        -
+            message: '#unknown class Grav\\Plugin\\Form\\Forms#'
+            path: '*/system/src/Grav/Common/Processors/PagesProcessor.php'
 
         # Can be ignored, after fopen there's always an $http_response_header locally available
         -