diff --git a/composer.json b/composer.json
index 9aa1914..35c3ce9 100644
--- a/composer.json
+++ b/composer.json
@@ -5,7 +5,7 @@
     "require": {
         "php": "^7.2",
         "symfony/dependency-injection": "^4.3 || ^5.0",
-        "symfony/http-kernel": "^4.3 || ^5.0",
+        "symfony/http-kernel": "^4.3 || ^5.1.5",
         "jeckel-lab/command-dispatcher": "^0.3",
         "symfony/config": "^4.3 || ^5.0",
         "symfony/doctrine-bridge": "^4.3 || ^5.0",
@@ -14,7 +14,7 @@
     ,
     "require-dev": {
         "roave/security-advisories": "dev-master",
-        "vimeo/psalm": "^3.8",
+        "vimeo/psalm": "^4.1",
         "phpmd/phpmd": "^2.8",
         "squizlabs/php_codesniffer": "^3.5",
         "phpro/grumphp": "^0.19.0"
diff --git a/psalm.xml b/psalm.xml
index 42f355b..4e9226b 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <psalm
-    totallyTyped="false"
+    errorLevel="2"
     resolveFromConfigFile="true"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
@@ -12,44 +12,4 @@
             <directory name="vendor" />
         </ignoreFiles>
     </projectFiles>
-
-    <issueHandlers>
-        <LessSpecificReturnType errorLevel="info" />
-
-        <!-- level 3 issues - slightly lazy code writing, but provably low false-negatives -->
-
-        <DeprecatedMethod errorLevel="info" />
-        <DeprecatedProperty errorLevel="info" />
-        <DeprecatedClass errorLevel="info" />
-        <DeprecatedConstant errorLevel="info" />
-        <DeprecatedFunction errorLevel="info" />
-        <DeprecatedInterface errorLevel="info" />
-        <DeprecatedTrait errorLevel="info" />
-
-        <InternalMethod errorLevel="info" />
-        <InternalProperty errorLevel="info" />
-        <InternalClass errorLevel="info" />
-
-        <MissingClosureReturnType errorLevel="info" />
-        <MissingReturnType errorLevel="info" />
-        <MissingPropertyType errorLevel="info" />
-        <InvalidDocblock errorLevel="info" />
-        <MisplacedRequiredParam errorLevel="info" />
-
-        <PropertyNotSetInConstructor errorLevel="info" />
-        <MissingConstructor errorLevel="info" />
-        <MissingClosureParamType errorLevel="info" />
-        <MissingParamType errorLevel="info" />
-
-        <RedundantCondition errorLevel="info" />
-
-        <DocblockTypeContradiction errorLevel="info" />
-        <RedundantConditionGivenDocblockType errorLevel="info" />
-
-        <UnresolvableInclude errorLevel="info" />
-
-        <RawObjectIteration errorLevel="info" />
-
-        <InvalidStringClass errorLevel="info" />
-    </issueHandlers>
 </psalm>
diff --git a/src/Compiler/CommandHandlerPass.php b/src/Compiler/CommandHandlerPass.php
index 112371b..1ae679f 100644
--- a/src/Compiler/CommandHandlerPass.php
+++ b/src/Compiler/CommandHandlerPass.php
@@ -41,15 +41,15 @@ public function process(ContainerBuilder $container): void
         $handlerMaps = [];
         // Find command handlers
         foreach (array_keys($container->findTaggedServiceIds($this->handlersTag)) as $serviceId) {
-            $classname = $container->getDefinition($serviceId)->getClass();
+            $classname = $container->getDefinition((string) $serviceId)->getClass();
             if (null === $classname) {
                 throw new RuntimeException(sprintf('Unable to find service with id: %s', $serviceId));
             }
 
             $aliasId = 'command_handler.handler.alias.' . $classname;
-            $container->setAlias($aliasId, $serviceId)->setPublic(true);
+            $container->setAlias($aliasId, (string) $serviceId)->setPublic(true);
 
-            /** @var array $commands */
+            /** @var string[] $commands */
             $commands = call_user_func([$classname, 'getHandledCommands']);
             foreach ($commands as $command) {
                 $handlerMaps[$command] = $aliasId;