diff --git a/src/Symfony/Component/Process/Process.php b/src/Symfony/Component/Process/Process.php
index 1c11505f07..5b6773540a 100644
--- a/src/Symfony/Component/Process/Process.php
+++ b/src/Symfony/Component/Process/Process.php
@@ -131,7 +131,7 @@ class Process
             $this->env = null;
         }
         $this->stdin = $stdin;
-        $this->timeout = $timeout;
+        $this->setTimeout($timeout);
         $this->enhanceWindowsCompatibility = true;
         $this->options = array_replace(array('suppress_errors' => true, 'binary_pipes' => true), $options);
     }
@@ -587,6 +587,12 @@ class Process
 
     public function setTimeout($timeout)
     {
+        $timeout = (integer) $timeout;
+
+        if ($timeout < 0) {
+            throw new \InvalidArgumentException('The timeout value must be a valid positive integer.');
+        }
+
         $this->timeout = $timeout;
     }
 
diff --git a/src/Symfony/Component/Process/ProcessBuilder.php b/src/Symfony/Component/Process/ProcessBuilder.php
index a1008e2b71..f9d2333d64 100644
--- a/src/Symfony/Component/Process/ProcessBuilder.php
+++ b/src/Symfony/Component/Process/ProcessBuilder.php
@@ -83,6 +83,12 @@ class ProcessBuilder
 
     public function setTimeout($timeout)
     {
+        $timeout = (integer) $timeout;
+
+        if ($timeout < 0) {
+            throw new \InvalidArgumentException('The timeout value must be a valid positive integer.');
+        }
+
         $this->timeout = $timeout;
 
         return $this;
diff --git a/src/Symfony/Component/Process/Tests/ProcessBuilderTest.php b/src/Symfony/Component/Process/Tests/ProcessBuilderTest.php
index 4e9c2e885e..fd9d620730 100644
--- a/src/Symfony/Component/Process/Tests/ProcessBuilderTest.php
+++ b/src/Symfony/Component/Process/Tests/ProcessBuilderTest.php
@@ -83,4 +83,13 @@ class ProcessBuilderTest extends \PHPUnit_Framework_TestCase
 
         $_ENV = $snapshot;
     }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     */
+    public function testNegativeTimeoutFromSetter()
+    {
+        $pb = new ProcessBuilder();
+        $pb->setTimeout(-1);
+    }
 }
diff --git a/src/Symfony/Component/Process/Tests/ProcessTest.php b/src/Symfony/Component/Process/Tests/ProcessTest.php
index dcaa3f4b59..354b3aea8a 100644
--- a/src/Symfony/Component/Process/Tests/ProcessTest.php
+++ b/src/Symfony/Component/Process/Tests/ProcessTest.php
@@ -18,6 +18,23 @@ use Symfony\Component\Process\Process;
  */
 class ProcessTest extends \PHPUnit_Framework_TestCase
 {
+    /**
+     * @expectedException \InvalidArgumentException
+     */
+    public function testNegativeTimeoutFromConstructor()
+    {
+        new Process('', null, null, null, -1);
+    }
+
+    /**
+     * @expectedException \InvalidArgumentException
+     */
+    public function testNegativeTimeoutFromSetter()
+    {
+        $p = new Process('');
+        $p->setTimeout(-1);
+    }
+
     /**
      * tests results from sub processes
      *