diff --git a/README.md b/README.md
index 2668ca0..b22fc37 100644
--- a/README.md
+++ b/README.md
@@ -159,6 +159,7 @@ return [
         //     'port' => '',
         //     'username' => '',
         //     'private_key' => '',
+        //     'private_key_path' => '',
         //     'passphrase' => '',
         //     'script_path' => '',
         // ],
diff --git a/config/task-runner.php b/config/task-runner.php
index cc4c75c..dce6a31 100644
--- a/config/task-runner.php
+++ b/config/task-runner.php
@@ -14,6 +14,7 @@
         //     'port' => '',
         //     'username' => '',
         //     'private_key' => '',
+        //     'private_key_path' => '',
         //     'passphrase' => '',
         //     'script_path' => '',
         // ],
diff --git a/src/Connection.php b/src/Connection.php
index 944a9d9..6b3780c 100644
--- a/src/Connection.php
+++ b/src/Connection.php
@@ -90,6 +90,10 @@ public static function fromArray(array $config): static
             $privateKey = $privateKey();
         }
 
+        if (! $privateKey && array_key_exists('private_key_path', $config)) {
+            $privateKey = file_get_contents($config['private_key_path']);
+        }
+
         return new static(
             host: $config['host'] ?: null,
             port: $config['port'] ?: null,
diff --git a/src/Helper.php b/src/Helper.php
index c560cee..82cf424 100644
--- a/src/Helper.php
+++ b/src/Helper.php
@@ -44,7 +44,7 @@ public static function temporaryDirectoryPath(string $pathOrFilename = ''): stri
     /**
      * Use the nohup command to run a script in the background.
      */
-    public static function scriptInBackground(string $scriptPath, string $outputPath = null, int $timeout = null): string
+    public static function scriptInBackground(string $scriptPath, ?string $outputPath = null, ?int $timeout = null): string
     {
         $outputPath = $outputPath ?: '/dev/null';
 
diff --git a/src/MakesTestAssertions.php b/src/MakesTestAssertions.php
index f20db06..e27ab16 100644
--- a/src/MakesTestAssertions.php
+++ b/src/MakesTestAssertions.php
@@ -7,7 +7,7 @@
 
 trait MakesTestAssertions
 {
-    public function assertDispatched(string|callable $taskClass, callable $additionalCallback = null): self
+    public function assertDispatched(string|callable $taskClass, ?callable $additionalCallback = null): self
     {
         $faked = $this->faked($this->makeAssertCallback($taskClass, $additionalCallback));
 
@@ -19,7 +19,7 @@ public function assertDispatched(string|callable $taskClass, callable $additiona
         return $this;
     }
 
-    public function assertNotDispatched(string|callable $taskClass, callable $additionalCallback = null): self
+    public function assertNotDispatched(string|callable $taskClass, ?callable $additionalCallback = null): self
     {
         $faked = $this->faked($this->makeAssertCallback($taskClass, $additionalCallback));
 
@@ -31,7 +31,7 @@ public function assertNotDispatched(string|callable $taskClass, callable $additi
         return $this;
     }
 
-    public function assertDispatchedTimes(string|callable $taskClass, int $times = 1, callable $additionalCallback = null): self
+    public function assertDispatchedTimes(string|callable $taskClass, int $times = 1, ?callable $additionalCallback = null): self
     {
         $count = $this->faked($this->makeAssertCallback($taskClass, $additionalCallback))->count();
 
@@ -44,7 +44,7 @@ public function assertDispatchedTimes(string|callable $taskClass, int $times = 1
         return $this;
     }
 
-    protected function typeNameOfFirstParameter(callable $callback = null): ?string
+    protected function typeNameOfFirstParameter(?callable $callback = null): ?string
     {
         if (! $callback) {
             return null;
@@ -61,14 +61,14 @@ protected function typeNameOfFirstParameter(callable $callback = null): ?string
         return $parameters[0]?->getType()?->getName() ?: null;
     }
 
-    protected function callbackExpectsPendingTask(callable $callback = null): bool
+    protected function callbackExpectsPendingTask(?callable $callback = null): bool
     {
         $typeName = $this->typeNameOfFirstParameter($callback);
 
         return ! $typeName || $typeName === PendingTask::class;
     }
 
-    protected function makeAssertCallback(string|callable $taskClass, callable $additionalCallback = null)
+    protected function makeAssertCallback(string|callable $taskClass, ?callable $additionalCallback = null)
     {
         if (! $additionalCallback) {
             $additionalCallback = fn () => true;
diff --git a/src/PendingTask.php b/src/PendingTask.php
index 5e1e9ae..2d81e0d 100644
--- a/src/PendingTask.php
+++ b/src/PendingTask.php
@@ -126,7 +126,7 @@ public function getId(): ?string
     /**
      * Sets the 'id' property.
      */
-    public function id(string $id = null): self
+    public function id(?string $id = null): self
     {
         $this->id = $id;
 
@@ -152,7 +152,7 @@ public function getOutputPath(): ?string
     /**
      * Sets the 'outputPath' property.
      */
-    public function writeOutputTo(string $outputPath = null): self
+    public function writeOutputTo(?string $outputPath = null): self
     {
         $this->outputPath = $outputPath;
 
@@ -162,7 +162,7 @@ public function writeOutputTo(string $outputPath = null): self
     /**
      * Checks if the given connection is the same as the connection of this task.
      */
-    public function shouldRunOnConnection(bool|string|Connection|callable $connection = null): bool
+    public function shouldRunOnConnection(bool|string|Connection|callable|null $connection = null): bool
     {
         if ($connection === null && $this->connection !== null) {
             return true;
@@ -207,7 +207,7 @@ public function storeInTemporaryDirectory(): string
     /**
      * Dispatches the task to the given task runner.
      */
-    public function dispatch(TaskDispatcher $taskDispatcher = null): ?ProcessOutput
+    public function dispatch(?TaskDispatcher $taskDispatcher = null): ?ProcessOutput
     {
         /** @var TaskDispatcher */
         $taskDispatcher = $taskDispatcher ?: app(TaskDispatcher::class);
diff --git a/src/ProcessOutput.php b/src/ProcessOutput.php
index c61b7ae..d9db9df 100644
--- a/src/ProcessOutput.php
+++ b/src/ProcessOutput.php
@@ -108,7 +108,7 @@ public function setIlluminateResult(ProcessResult $result): self
     /**
      * Setter for the exit code.
      */
-    public function setExitCode(int $exitCode = null): self
+    public function setExitCode(?int $exitCode = null): self
     {
         $this->exitCode = $exitCode;
 
diff --git a/src/ProcessRunner.php b/src/ProcessRunner.php
index c0aea1b..dd1a986 100644
--- a/src/ProcessRunner.php
+++ b/src/ProcessRunner.php
@@ -10,7 +10,7 @@ class ProcessRunner
     /**
      * Runs the given process and waits for it to finish.
      */
-    public function run(PendingProcess $process, callable $onOutput = null): ProcessOutput
+    public function run(PendingProcess $process, ?callable $onOutput = null): ProcessOutput
     {
         $output = new ProcessOutput;
 
diff --git a/tests/ConnectionTest.php b/tests/ConnectionTest.php
index 31b8219..631d1e6 100644
--- a/tests/ConnectionTest.php
+++ b/tests/ConnectionTest.php
@@ -2,13 +2,14 @@
 
 use ProtoneMedia\LaravelTaskRunner\Connection;
 
-function addConnectionToConfig()
+function addConnectionToConfig($callable = true, $path = false)
 {
     config(['task-runner.connections.production' => [
         'host' => '1.1.1.1',
         'port' => '21',
         'username' => 'root',
-        'private_key' => fn () => 'secret',
+        'private_key' => $callable ? fn () => 'secret' : null,
+        'private_key_path' => $path ? __DIR__.'/private_key' : null,
         'passphrase' => 'password',
         'script_path' => '',
     ]]);
@@ -21,3 +22,11 @@ function addConnectionToConfig()
 
     expect($connection->privateKey)->toBe('secret');
 });
+
+it('can resolve a private key from a path', function () {
+    addConnectionToConfig(callable: false, path: true);
+
+    $connection = Connection::fromConfig('production');
+
+    expect($connection->privateKey)->toBe('secret2');
+});
diff --git a/tests/private_key b/tests/private_key
new file mode 100644
index 0000000..ee90847
--- /dev/null
+++ b/tests/private_key
@@ -0,0 +1 @@
+secret2
\ No newline at end of file