diff --git a/src/applications/phrequent/storage/PhrequentTimeSlices.php b/src/applications/phrequent/storage/PhrequentTimeSlices.php
index 30c4345720..b19f857149 100644
--- a/src/applications/phrequent/storage/PhrequentTimeSlices.php
+++ b/src/applications/phrequent/storage/PhrequentTimeSlices.php
@@ -17,13 +17,15 @@ final class PhrequentTimeSlices extends Phobject {
   }
 
   public function getDuration($now) {
+    $total = 0;
     foreach ($this->ranges as $range) {
       if ($range[1] === null) {
-        return $now - $range[0];
+        $total += $now - $range[0];
       } else {
-        return $range[1] - $range[0];
+        $total += $range[1] - $range[0];
       }
     }
+    return $total;
   }
 
   public function getIsOngoing() {
diff --git a/src/applications/phrequent/storage/__tests__/PhrequentTimeBlockTestCase.php b/src/applications/phrequent/storage/__tests__/PhrequentTimeBlockTestCase.php
index d42560090e..b2e062a8e8 100644
--- a/src/applications/phrequent/storage/__tests__/PhrequentTimeBlockTestCase.php
+++ b/src/applications/phrequent/storage/__tests__/PhrequentTimeBlockTestCase.php
@@ -282,6 +282,30 @@ final class PhrequentTimeBlockTestCase extends PhabricatorTestCase {
       $ranges);
   }
 
+  public function testSumTimeSlices() {
+    // This block has multiple closed slices.
+    $block = new PhrequentTimeBlock(
+      array(
+        $this->newEvent('T1', 3456, 4456)->attachPreemptingEvents(array()),
+        $this->newEvent('T1', 8000, 9000)->attachPreemptingEvents(array()),
+      ));
+
+    $this->assertEqual(
+      2000,
+      $block->getTimeSpentOnObject('T1', 10000));
+
+    // This block has an open slice.
+    $block = new PhrequentTimeBlock(
+      array(
+        $this->newEvent('T1', 3456, 4456)->attachPreemptingEvents(array()),
+        $this->newEvent('T1', 8000, null)->attachPreemptingEvents(array()),
+      ));
+
+    $this->assertEqual(
+      3000,
+      $block->getTimeSpentOnObject('T1', 10000));
+  }
+
   private function newEvent($object_phid, $start_time, $end_time) {
     static $id = 0;