diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb54c41..6d63a7e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,9 @@
 Latest
 ------
 
+### Fixes
+* [#75](https://github.com/cleverage/flysystem-process-bundle/issues/75) `FileFetchTask` (`flysystem_file_fetch`): an unknown storage fails at initialization with an explicit message (`Unknown storage "…" (option "…")`, with the known storages) instead of `Service "…" not found`, When the task is executed after a failed initialization (process-bundle v5 goes on), it fails with an explicit message instead of `Typed property … must not be accessed before initialization`. Update documentation, add tests.
+
 v3.3
 ------
 
diff --git a/docs/reference/tasks/file_fetch_task.md b/docs/reference/tasks/file_fetch_task.md
index e3f2340..6f24c03 100644
--- a/docs/reference/tasks/file_fetch_task.md
+++ b/docs/reference/tasks/file_fetch_task.md
@@ -98,7 +98,9 @@ Notes
 -----
 
 * Both storages are resolved when the task is initialized, at the start of the process: an unknown storage name makes
-  the process fail before any task is executed.
+  the initialization fail (`Unknown storage "…"`, logged at the `critical` level). With process-bundle v5, the process
+  goes on and fails when the task is first executed (deprecated, the process will fail before executing any task in
+  process-bundle v6).
 * `file_pattern` is only tested on the files located at the root of `source_filesystem` (the listing is not
   recursive and directories are ignored). The pattern is tested on the path relative to the storage root: to target
   a sub-directory, configure a dedicated storage whose root is this directory.
diff --git a/src/Task/FileFetchTask.php b/src/Task/FileFetchTask.php
index 7190e76..a198f47 100644
--- a/src/Task/FileFetchTask.php
+++ b/src/Task/FileFetchTask.php
@@ -19,6 +19,7 @@
 use CleverAge\ProcessBundle\Model\ProcessState;
 use League\Flysystem\FilesystemException;
 use League\Flysystem\FilesystemOperator;
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
 use Symfony\Component\DependencyInjection\ServiceLocator;
 use Symfony\Component\OptionsResolver\OptionsResolver;
 
@@ -50,6 +51,7 @@ public function __construct(protected readonly ServiceLocator $storages)
 
     /**
      * @throws \InvalidArgumentException
+     * @throws UnexpectedValueException
      */
     #[\Override]
     public function initialize(ProcessState $state): void
@@ -57,12 +59,8 @@ public function initialize(ProcessState $state): void
         // Configure options
         parent::initialize($state);
 
-        /** @var string $sourceFilesystemOption */
-        $sourceFilesystemOption = $this->getOption($state, 'source_filesystem');
-        $this->sourceFS = $this->storages->get($sourceFilesystemOption);
-        /** @var string $destinationFilesystemOption */
-        $destinationFilesystemOption = $this->getOption($state, 'destination_filesystem');
-        $this->destinationFS = $this->storages->get($destinationFilesystemOption);
+        $this->sourceFS = $this->getStorage($state, 'source_filesystem');
+        $this->destinationFS = $this->getStorage($state, 'destination_filesystem');
     }
 
     /**
@@ -72,6 +70,11 @@ public function initialize(ProcessState $state): void
      */
     public function execute(ProcessState $state): void
     {
+        // With process-bundle v5, a task is executed even if its initialization has failed (the error is logged)
+        if (!isset($this->sourceFS, $this->destinationFS)) {
+            throw new UnexpectedValueException('The storages of the task are not available: its initialization has failed, see the previous error');
+        }
+
         // The files are listed once per input, when its iteration starts
         $this->matchingFiles ??= $this->findMatchingFiles($state);
 
@@ -104,6 +107,20 @@ public function next(ProcessState $state): bool
         return false;
     }
 
+    /**
+     * @throws UnexpectedValueException
+     */
+    protected function getStorage(ProcessState $state, string $option): FilesystemOperator
+    {
+        /** @var string $storage */
+        $storage = $this->getOption($state, $option);
+        try {
+            return $this->storages->get($storage);
+        } catch (ServiceNotFoundException $e) {
+            throw new UnexpectedValueException(\sprintf('Unknown storage "%s" (option "%s"), known storages: "%s"', $storage, $option, implode('", "', array_keys($this->storages->getProvidedServices()))), 0, $e);
+        }
+    }
+
     /**
      * @return list<string>
      *
diff --git a/tests/Task/FileFetchTaskStorageTest.php b/tests/Task/FileFetchTaskStorageTest.php
index 316ae59..7349352 100644
--- a/tests/Task/FileFetchTaskStorageTest.php
+++ b/tests/Task/FileFetchTaskStorageTest.php
@@ -13,6 +13,7 @@
 
 namespace CleverAge\FlysystemProcessBundle\Tests\Task;
 
+use CleverAge\FlysystemProcessBundle\Exception\UnexpectedValueException;
 use CleverAge\FlysystemProcessBundle\Task\FileFetchTask;
 use CleverAge\ProcessBundle\Model\ProcessState;
 use PHPUnit\Framework\Attributes\CoversClass;
@@ -143,7 +144,8 @@ public function testNextBeforeExecute(): void
 
     public function testUnknownStorage(): void
     {
-        $this->expectException(\Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException::class);
+        $this->expectException(UnexpectedValueException::class);
+        $this->expectExceptionMessage('Unknown storage "unknown" (option "source_filesystem")');
         $this->createTask(['source_filesystem' => 'unknown']);
     }
 
diff --git a/tests/Task/FileFetchTaskTest.php b/tests/Task/FileFetchTaskTest.php
index 86bf533..0bd010f 100644
--- a/tests/Task/FileFetchTaskTest.php
+++ b/tests/Task/FileFetchTaskTest.php
@@ -13,6 +13,7 @@
 
 namespace CleverAge\FlysystemProcessBundle\Tests\Task;
 
+use CleverAge\FlysystemProcessBundle\Exception\UnexpectedValueException;
 use CleverAge\FlysystemProcessBundle\Task\FileFetchTask;
 use CleverAge\ProcessBundle\Model\ProcessState;
 use League\Flysystem\FilesystemOperator;
@@ -64,6 +65,31 @@ public function testWriteFailureKeepsSourceAndFails(): void
         $task->execute($state);
     }
 
+    public function testUnknownStorageFailsAtInitialization(): void
+    {
+        $task = $this->createTask();
+
+        $this->expectException(UnexpectedValueException::class);
+        $this->expectExceptionMessage('Unknown storage "unknown" (option "destination_filesystem"), known storages: "source", "destination"');
+        $task->initialize($this->createState('unknown'));
+    }
+
+    public function testTaskFailsExplicitlyWhenExecutedAfterAFailedInitialization(): void
+    {
+        $state = $this->createState('unknown');
+        $task = $this->createTask();
+        try {
+            $task->initialize($state);
+            self::fail('The initialization should have failed');
+        } catch (UnexpectedValueException) {
+        }
+
+        $this->destination->expects($this->never())->method('writeStream');
+        $this->expectException(UnexpectedValueException::class);
+        $this->expectExceptionMessage('The storages of the task are not available: its initialization has failed, see the previous error');
+        $task->execute($state);
+    }
+
     private function createTask(): FileFetchTask
     {
         /** @var ServiceLocator<FilesystemOperator> $storages */
@@ -75,12 +101,12 @@ private function createTask(): FileFetchTask
         return new FileFetchTask($storages);
     }
 
-    private function createState(): ProcessState&MockObject
+    private function createState(string $destination = 'destination'): ProcessState&MockObject
     {
         $state = $this->createMock(ProcessState::class);
         $state->method('getContextualizedOptions')->willReturn([
             'source_filesystem' => 'source',
-            'destination_filesystem' => 'destination',
+            'destination_filesystem' => $destination,
             'remove_source' => true,
         ]);
         $state->method('getInput')->willReturn('file.txt');