diff --git a/psalm.xml b/psalm.xml
index 70602d3..e55d59b 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -31,5 +31,10 @@
 				<referencedClass name="Doctrine\DBAL\Schema\Table" />
 			</errorLevel>
 		</UndefinedDocblockClass>
+		<InvalidReturnType>
+			<errorLevel type="suppress">
+				<directory name="stubs" />
+			</errorLevel>
+		</InvalidReturnType>
 	</issueHandlers>
 </psalm>
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php
index 0029ed4..655dcd5 100644
--- a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php
@@ -17,28 +17,75 @@ namespace OCA\GPodderSync\Core\EpisodeAction;
  *  id: int
  * }
  */
-interface EpisodeAction
+class EpisodeAction
 {
-	public function getPodcast(): string;
+	/**
+	 * @return string
+	 */
+	public function getPodcast()
+	{
+	}
 
-	public function getEpisode(): string;
+	/**
+	 * @return string
+	 */
+	public function getEpisode()
+	{
+	}
 
-	public function getAction(): string;
+	/**
+	 * @return string
+	 */
+	public function getAction()
+	{
+	}
 
-	public function getTimestamp(): string;
+	/**
+	 * @return string
+	 */
+	public function getTimestamp()
+	{
+	}
 
-	public function getStarted(): int;
+	/**
+	 * @return int
+	 */
+	public function getStarted()
+	{
+	}
 
-	public function getPosition(): int;
+	/**
+	 * @return int
+	 */
+	public function getPosition()
+	{
+	}
 
-	public function getTotal(): int;
+	/**
+	 * @return int
+	 */
+	public function getTotal()
+	{
+	}
 
-	public function getGuid(): ?string;
+	/**
+	 * @return ?string
+	 */
+	public function getGuid()
+	{
+	}
 
-	public function getId(): int;
+	/**
+	 * @return int
+	 */
+	public function getId()
+	{
+	}
 
 	/**
 	 * @return EpisodeActionType
 	 */
-	public function toArray(): array;
+	public function toArray()
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php
index 403a071..2a2df04 100644
--- a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php
@@ -4,12 +4,14 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\EpisodeAction;
 
-interface EpisodeActionReader
+class EpisodeActionReader
 {
 	/**
 	 * @param  array                     $episodeActionsArray []
 	 * @return EpisodeAction[]
 	 * @throws \InvalidArgumentException
 	 */
-	public function fromArray(array $episodeActionsArray): array;
+	public function fromArray(array $episodeActionsArray)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php
index b0da7a6..843922d 100644
--- a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php
@@ -4,7 +4,12 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\EpisodeAction;
 
-interface EpisodeActionSaver
+class EpisodeActionSaver
 {
-	public function saveEpisodeActions(array $episodeActionsArray, string $userId): array;
+	/**
+	 * @return array
+	 */
+	public function saveEpisodeActions(array $episodeActionsArray, string $userId)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php
index 5a261f0..47eec74 100644
--- a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php
@@ -13,17 +13,23 @@ namespace OCA\GPodderSync\Core\PodcastData;
  *  play: int
  * }
  */
-interface PodcastActionCounts extends \JsonSerializable
+class PodcastActionCounts implements \JsonSerializable
 {
-	public function incrementAction(string $action): void;
+	public function incrementAction(string $action): void
+	{
+	}
 
 	/**
 	 * @return PodcastActionCountsType
 	 */
-	public function toArray(): array;
+	public function toArray()
+	{
+	}
 
 	/**
 	 * @return PodcastActionCountsType
 	 */
-	public function jsonSerialize(): array;
+	public function jsonSerialize(): mixed
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php
index db27f8c..1bfefe2 100644
--- a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php
@@ -15,43 +15,88 @@ namespace OCA\GPodderSync\Core\PodcastData;
  *  imageBlob: ?string
  * }
  */
-interface PodcastData extends \JsonSerializable
+class PodcastData implements \JsonSerializable
 {
-	public function __toString(): string;
+	/**
+	 * @return PodcastData
+	 * @throws \Exception  if the XML data could not be parsed
+	 */
+	public static function parseRssXml(string $xmlString, ?int $fetchedAtUnix = null)
+	{
+	}
 
 	/**
-	 * @throws \Exception if the XML data could not be parsed
+	 * @return ?string
 	 */
-	public static function parseRssXml(string $xmlString, ?int $fetchedAtUnix = null): PodcastData;
+	public function getTitle()
+	{
+	}
 
-	public function getTitle(): ?string;
+	/**
+	 * @return ?string
+	 */
+	public function getAuthor()
+	{
+	}
 
-	public function getAuthor(): ?string;
+	/**
+	 * @return ?string
+	 */
+	public function getLink()
+	{
+	}
 
-	public function getLink(): ?string;
+	/**
+	 * @return ?string
+	 */
+	public function getDescription()
+	{
+	}
 
-	public function getDescription(): ?string;
+	/**
+	 * @return ?string
+	 */
+	public function getImageUrl()
+	{
+	}
 
-	public function getImageUrl(): ?string;
+	/**
+	 * @return ?int
+	 */
+	public function getFetchedAtUnix()
+	{
+	}
 
-	public function getFetchedAtUnix(): ?int;
+	/**
+	 * @return ?string
+	 */
+	public function getImageBlob()
+	{
+	}
 
-	public function getImageBlob(): ?string;
-
-	public function setImageBlob(?string $blob): void;
+	public function setImageBlob(?string $blob): void
+	{
+	}
 
 	/**
 	 * @return PodcastDataType
 	 */
-	public function toArray(): array;
+	public function toArray()
+	{
+	}
 
 	/**
 	 * @return PodcastDataType
 	 */
-	public function jsonSerialize(): array;
+	public function jsonSerialize(): mixed
+	{
+	}
 
 	/**
-	 * @param PodcastDataType $data
+	 * @param  PodcastDataType $data
+	 * @return PodcastData
 	 */
-	public static function fromArray(array $data): PodcastData;
+	public static function fromArray(array $data)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php
index 06f6dbf..7b536c1 100644
--- a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php
@@ -4,13 +4,33 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\PodcastData;
 
-interface PodcastDataReader
+class PodcastDataReader
 {
-	public function getCachedOrFetchPodcastData(string $url, string $userId): ?PodcastData;
+	/**
+	 * @return ?PodcastData
+	 */
+	public function getCachedOrFetchPodcastData(string $url, string $userId)
+	{
+	}
 
-	public function fetchPodcastData(string $url, string $userId): ?PodcastData;
+	/**
+	 * @return ?PodcastData
+	 */
+	public function fetchPodcastData(string $url, string $userId)
+	{
+	}
 
-	public function tryGetCachedPodcastData(string $url): ?PodcastData;
+	/**
+	 * @return ?PodcastData
+	 */
+	public function tryGetCachedPodcastData(string $url)
+	{
+	}
 
-	public function trySetCachedPodcastData(string $url, PodcastData $data): bool;
+	/**
+	 * @return bool
+	 */
+	public function trySetCachedPodcastData(string $url, PodcastData $data)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php
index db2ded6..ce7e0c9 100644
--- a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php
@@ -11,23 +11,44 @@ namespace OCA\GPodderSync\Core\PodcastData;
  *  actionCounts: PodcastActionCounts
  * }
  */
-interface PodcastMetrics extends \JsonSerializable
+class PodcastMetrics implements \JsonSerializable
 {
-	public function getUrl(): string;
+	/**
+	 * @return string
+	 */
+	public function getUrl()
+	{
+	}
 
-	public function getActionCounts(): PodcastActionCounts;
+	/**
+	 * @return PodcastActionCounts
+	 */
+	public function getActionCounts()
+	{
+	}
 
-	public function getListenedSeconds(): int;
+	/**
+	 * @return int
+	 */
+	public function getListenedSeconds()
+	{
+	}
 
-	public function addListenedSeconds(int $seconds): void;
+	public function addListenedSeconds(int $seconds): void
+	{
+	}
 
 	/**
 	 * @return PodcastMetricsType
 	 */
-	public function toArray(): array;
+	public function toArray()
+	{
+	}
 
 	/**
 	 * @return PodcastMetricsType
 	 */
-	public function jsonSerialize(): array;
+	public function jsonSerialize(): mixed
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php
index 0cceba1..212282d 100644
--- a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php
@@ -4,10 +4,12 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\PodcastData;
 
-interface PodcastMetricsReader
+class PodcastMetricsReader
 {
 	/**
 	 * @return PodcastMetrics[]
 	 */
-	public function metrics(string $userId): array;
+	public function metrics(string $userId)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php
index 9a9d480..7ef7f85 100644
--- a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php
@@ -4,11 +4,19 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\SubscriptionChange;
 
-interface SubscriptionChange
+class SubscriptionChange
 {
-	public function __toString(): string;
+	/**
+	 * @return bool
+	 */
+	public function isSubscribed()
+	{
+	}
 
-	public function isSubscribed(): bool;
-
-	public function getUrl(): string;
+	/**
+	 * @return string
+	 */
+	public function getUrl()
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php
index f41edde..eef272f 100644
--- a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php
@@ -4,10 +4,12 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\SubscriptionChange;
 
-interface SubscriptionChangeRequestParser
+class SubscriptionChangeRequestParser
 {
 	/**
 	 * @return SubscriptionChange[]
 	 */
-	public function createSubscriptionChangeList(array $urlsSubscribed, array $urlsUnsubscribed): array;
+	public function createSubscriptionChangeList(array $urlsSubscribed, array $urlsUnsubscribed)
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php
index 7720d92..a258073 100644
--- a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php
@@ -4,7 +4,9 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\SubscriptionChange;
 
-interface SubscriptionChangeSaver
+class SubscriptionChangeSaver
 {
-	public function saveSubscriptionChanges(array $urlsSubscribed, array $urlsUnsubscribed, string $userId): void;
+	public function saveSubscriptionChanges(array $urlsSubscribed, array $urlsUnsubscribed, string $userId): void
+	{
+	}
 }
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php
index 4b833ad..e0ee4f5 100644
--- a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php
@@ -4,10 +4,12 @@ declare(strict_types=1);
 
 namespace OCA\GPodderSync\Core\SubscriptionChange;
 
-interface SubscriptionChangesReader
+class SubscriptionChangesReader
 {
 	/**
 	 * @return SubscriptionChange[]
 	 */
-	public static function mapToSubscriptionsChanges(array $urls, bool $subscribed): array;
+	public static function mapToSubscriptionsChanges(array $urls, bool $subscribed)
+	{
+	}
 }