diff --git a/core/lib/Drupal/Core/TypedData/Type/DurationInterface.php b/core/lib/Drupal/Core/TypedData/Type/DurationInterface.php
index a39c0d5..56d3b51 100644
--- a/core/lib/Drupal/Core/TypedData/Type/DurationInterface.php
+++ b/core/lib/Drupal/Core/TypedData/Type/DurationInterface.php
@@ -19,6 +19,8 @@
    *
    * @return \DateInterval|null
    *   A DateInterval object or NULL if there is no duration.
+   *
+   * @throws \Exception
    */
   public function getDuration();
 
diff --git a/core/lib/Drupal/Core/TypedData/Type/TimeSpan.php b/core/lib/Drupal/Core/TypedData/Type/TimeSpan.php
index c70a064..be540e1 100644
--- a/core/lib/Drupal/Core/TypedData/Type/TimeSpan.php
+++ b/core/lib/Drupal/Core/TypedData/Type/TimeSpan.php
@@ -22,7 +22,7 @@ class TimeSpan extends Integer implements DurationInterface {
    */
   public function getDuration() {
     if ($this->value) {
-      return new DateInterval('PT' . $this->value . 'S');
+      return new \DateInterval('PT' . $this->value . 'S');
     }
   }
 
diff --git a/core/lib/Drupal/Core/TypedData/Type/Timestamp.php b/core/lib/Drupal/Core/TypedData/Type/Timestamp.php
index 86ac13c..74ae3b1 100644
--- a/core/lib/Drupal/Core/TypedData/Type/Timestamp.php
+++ b/core/lib/Drupal/Core/TypedData/Type/Timestamp.php
@@ -35,6 +35,6 @@ public function getDateTime() {
    * {@inheritdoc}
    */
   public function setDateTime(DrupalDateTime $dateTime) {
-    $this->value = $dateTime->format('c');
+    $this->value = $dateTime->getTimestamp();
   }
 }
diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
index 0547991..3a522b6 100644
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
@@ -54,10 +54,15 @@ public function validate($value, Constraint $constraint) {
       $valid = FALSE;
     }
     // @todo: Move those to separate constraint validators.
-    if ($typed_data instanceof DateTimeInterface && $typed_data->getDateTime()->hasErrors()) {
-      $valid = FALSE;
-    }
-    if ($typed_data instanceof DurationInterface && !($typed_data->getDuration() instanceof DateInterval)) {
+    try {
+      if ($typed_data instanceof DateTimeInterface && $typed_data->getDateTime()->hasErrors()) {
+        $valid = FALSE;
+      }
+      if ($typed_data instanceof DurationInterface && !($typed_data->getDuration() instanceof DateInterval)) {
+        $valid = FALSE;
+      }
+    } catch (\Exception $e) {
+      // Invalid durations or dates might throw exceptions.
       $valid = FALSE;
     }
 
diff --git a/core/modules/datetime/lib/Drupal/datetime/Type/DateTimeItem.php b/core/modules/datetime/lib/Drupal/datetime/Type/DateTimeItem.php
index 2fe97e4..78c1824 100644
--- a/core/modules/datetime/lib/Drupal/datetime/Type/DateTimeItem.php
+++ b/core/modules/datetime/lib/Drupal/datetime/Type/DateTimeItem.php
@@ -30,7 +30,7 @@ public function getPropertyDefinitions() {
 
     if (!isset(self::$propertyDefinitions)) {
       self::$propertyDefinitions['value'] = array(
-        'type' => 'datetime',
+        'type' => 'datetime_iso8601',
         'label' => t('Date value'),
       );
     }
diff --git a/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
index ad81618..630d027 100644
--- a/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/TypedData/TypedDataTest.php
@@ -182,10 +182,10 @@ public function testGetAndSet() {
     // DurationIso8601 type.
     $value = 'PT20S';
     $typed_data = $this->createTypedData(array('type' => 'duration_iso8601'), $value);
-    $this->assertTrue($typed_data->getValue() === $value, 'DurationIso8601 value was fetched.');
+    $this->assertIdentical($typed_data->getValue(), $value, 'DurationIso8601 value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue('P40D');
-    $this->assertTrue($typed_data->getValue()->d == 40, 'DurationIso8601 value was changed and set by duration string.');
+    $this->assertEqual($typed_data->getDuration()->d, 40, 'DurationIso8601 value was changed and set by duration string.');
     $this->assertTrue(is_string($typed_data->getString()), 'DurationIso8601 value was converted to string');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
@@ -197,17 +197,20 @@ public function testGetAndSet() {
     $typed_data = $this->createTypedData(array('type' => 'duration_iso8601'), 'PT20S');
     $this->assertTrue($typed_data->getDuration() instanceof DateInterval);
     $typed_data->setDuration(new DateInterval('P40D'));
-    $this->assertEqual($typed_data->getValue(), 'P40D');
+    // @todo: Should we make this "nicer"?
+    $this->assertEqual($typed_data->getValue(), 'P0Y0M40DT0H0M0S');
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getDuration());
 
     // Time span type.
-    $value = new DateInterval(20);
+    $value = 20;
     $typed_data = $this->createTypedData(array('type' => 'timespan'), $value);
-    $this->assertTrue($typed_data->getValue() === $value, 'Time span value was fetched.');
+    $this->assertIdentical($typed_data->getValue(), $value, 'Time span value was fetched.');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(60 * 60 * 4);
-    $this->assertTrue($typed_data->getDuration()->h == 4, 'Time span was changed');
+    // @todo: DateInterval does not recalculate the components, should the time
+    //   span class take care of this?
+    $this->assertEqual($typed_data->getDuration()->s, 14400, 'Time span was changed');
     $this->assertTrue(is_string($typed_data->getString()), 'Time span value was converted to string');
     $this->assertEqual($typed_data->validate()->count(), 0);
     $typed_data->setValue(NULL);
@@ -218,7 +221,7 @@ public function testGetAndSet() {
     // Check implementation of DurationInterface.
     $typed_data = $this->createTypedData(array('type' => 'timespan'), 20);
     $this->assertTrue($typed_data->getDuration() instanceof DateInterval);
-    $typed_data->setDuration(new DateInterval('P40H'));
+    $typed_data->setDuration(new DateInterval('PT4H'));
     $this->assertEqual($typed_data->getValue(), 60 * 60 * 4);
     $typed_data->setValue(NULL);
     $this->assertNull($typed_data->getDuration());