diff --git a/appinfo/info.xml b/appinfo/info.xml
index 0df513a0..aa1f0c2b 100644
--- a/appinfo/info.xml
+++ b/appinfo/info.xml
@@ -14,8 +14,8 @@
 	<namespace>Recommendations</namespace>
 	<category>office</category>
 	<dependencies>
-		<php min-version="7.0" max-version="7.3"/>
-		<nextcloud min-version="15" max-version="16"/>
+		<php min-version="7.1" max-version="7.3"/>
+		<nextcloud min-version="16" max-version="16"/>
 	</dependencies>
 	<commands>
 		<command>\OCA\Recommendations\Command\GetRecommendations</command>
diff --git a/lib/AppInfo/Application.php b/lib/AppInfo/Application.php
index 5abe0aad..d5dedbb0 100644
--- a/lib/AppInfo/Application.php
+++ b/lib/AppInfo/Application.php
@@ -30,7 +30,7 @@
 
 class Application extends App {
 
-	const APP_ID = 'recommendations';
+	public const APP_ID = 'recommendations';
 
 	public function __construct(array $urlParams = []) {
 		parent::__construct(self::APP_ID, $urlParams);
diff --git a/lib/Service/IRecommendation.php b/lib/Service/IRecommendation.php
index 036bc6ff..3b61f7ff 100644
--- a/lib/Service/IRecommendation.php
+++ b/lib/Service/IRecommendation.php
@@ -36,7 +36,7 @@ public function getTimestamp(): int;
 
 	public function getNode(): Node;
 
-	public function hasPreview();
+	public function hasPreview(): bool;
 
 	public function setHasPreview(bool $state);
 
diff --git a/lib/Service/RecommendationService.php b/lib/Service/RecommendationService.php
index 1569f01b..d830b8b1 100644
--- a/lib/Service/RecommendationService.php
+++ b/lib/Service/RecommendationService.php
@@ -34,7 +34,7 @@
 
 class RecommendationService {
 
-	const MAX_RECOMMENDATIONS = 5;
+	private const MAX_RECOMMENDATIONS = 5;
 
 	/** @var IRecommendationSource */
 	private $sources;
diff --git a/lib/Service/RecommendedFile.php b/lib/Service/RecommendedFile.php
index 60767107..cb20b3d1 100644
--- a/lib/Service/RecommendedFile.php
+++ b/lib/Service/RecommendedFile.php
@@ -75,7 +75,7 @@ public function getReason(): string {
 		return $this->reason;
 	}
 
-	public function hasPreview() {
+	public function hasPreview(): bool {
 		return $this->hasPreview;
 	}