diff --git a/src/applications/maniphest/editor/ManiphestEditEngine.php b/src/applications/maniphest/editor/ManiphestEditEngine.php
--- a/src/applications/maniphest/editor/ManiphestEditEngine.php
+++ b/src/applications/maniphest/editor/ManiphestEditEngine.php
@@ -58,17 +58,9 @@
       unset($status_map[$dup_status]);
     }
 
-    $owner_phid = $object->getOwnerPHID();
-    if ($owner_phid) {
-      $owner_value = array($owner_phid);
-    } else {
-      $owner_value = array();
-    }
-
     $priority_map = ManiphestTaskPriority::getTaskPriorityMap();
 
     // TODO: Restore these or toss them:
-    // - Require a single owner.
     // - Default owner to viewer.
     // - Don't show "change status" for closed tasks.
     // - Don't show "change owner" for closed tasks.
@@ -92,12 +84,12 @@
         ->setValue($object->getStatus())
         ->setOptions($status_map),
       id(new PhabricatorUsersEditField())
-        ->setKey('assigned')
-        ->setAliases(array('assign', 'assignee'))
+        ->setKey('owner')
+        ->setAliases(array('ownerPHID', 'assign', 'assigned'))
         ->setLabel(pht('Assigned To'))
         ->setDescription(pht('User who is responsible for the task.'))
         ->setTransactionType(ManiphestTransaction::TYPE_OWNER)
-        ->setValue($owner_value),
+        ->setSingleValue($object->getOwnerPHID()),
       id(new PhabricatorSelectEditField())
         ->setKey('priority')
         ->setLabel(pht('Priority'))
diff --git a/src/applications/transactions/editfield/PhabricatorPHIDListEditField.php b/src/applications/transactions/editfield/PhabricatorPHIDListEditField.php
--- a/src/applications/transactions/editfield/PhabricatorPHIDListEditField.php
+++ b/src/applications/transactions/editfield/PhabricatorPHIDListEditField.php
@@ -5,6 +5,7 @@
 
   private $useEdgeTransactions;
   private $transactionDescriptions = array();
+  private $isSingleValue;
 
   public function setUseEdgeTransactions($use_edge_transactions) {
     $this->useEdgeTransactions = $use_edge_transactions;
@@ -24,6 +25,21 @@
     return $this;
   }
 
+  public function setSingleValue($value) {
+    if ($value === null) {
+      $value = array();
+    } else {
+      $value = array($value);
+    }
+
+    $this->isSingleValue = true;
+    return $this->setValue($value);
+  }
+
+  public function getIsSingleValue() {
+    return $this->isSingleValue;
+  }
+
   protected function newHTTPParameterType() {
     return new AphrontPHIDListHTTPParameterType();
   }
@@ -31,6 +47,14 @@
   public function getValueForTransaction() {
     $new = parent::getValueForTransaction();
 
+    if ($this->getIsSingleValue()) {
+      if ($new) {
+        return head($new);
+      } else {
+        return null;
+      }
+    }
+
     if (!$this->getUseEdgeTransactions()) {
       return $new;
     }
@@ -68,7 +92,13 @@
       return new PhabricatorEdgeEditType();
     }
 
-    return parent::newEditType();
+    $type = parent::newEditType();
+
+    if ($this->getIsSingleValue()) {
+      $type->setValueType('phid');
+    }
+
+    return $type;
   }
 
   public function getConduitEditTypes() {
diff --git a/src/applications/transactions/editfield/PhabricatorTokenizerEditField.php b/src/applications/transactions/editfield/PhabricatorTokenizerEditField.php
--- a/src/applications/transactions/editfield/PhabricatorTokenizerEditField.php
+++ b/src/applications/transactions/editfield/PhabricatorTokenizerEditField.php
@@ -25,6 +25,10 @@
       $control->setOriginalValue($initial_value);
     }
 
+    if ($this->getIsSingleValue()) {
+      $control->setLimit(1);
+    }
+
     return $control;
   }