diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -999,7 +999,31 @@
           $xaction->setPHID($xaction->generatePHID());
           $comment_editor->applyEdit($xaction, $xaction->getComment());
         } else {
-          $xaction->save();
+
+          // TODO: This is a transitional hack to let us migrate edge
+          // transactions to a more efficient storage format. For now, we're
+          // going to write a new slim format to the database but keep the old
+          // bulky format on the objects so we don't have to upgrade all the
+          // edit logic to the new format yet. See T13051.
+
+          $edge_type = PhabricatorTransactions::TYPE_EDGE;
+          if ($xaction->getTransactionType() == $edge_type) {
+            $bulky_old = $xaction->getOldValue();
+            $bulky_new = $xaction->getNewValue();
+
+            $record = PhabricatorEdgeChangeRecord::newFromTransaction($xaction);
+            $slim_old = $record->getModernOldEdgeTransactionData();
+            $slim_new = $record->getModernNewEdgeTransactionData();
+
+            $xaction->setOldValue($slim_old);
+            $xaction->setNewValue($slim_new);
+            $xaction->save();
+
+            $xaction->setOldValue($bulky_old);
+            $xaction->setNewValue($bulky_new);
+          } else {
+            $xaction->save();
+          }
         }
       }
 
diff --git a/src/infrastructure/edges/util/PhabricatorEdgeChangeRecord.php b/src/infrastructure/edges/util/PhabricatorEdgeChangeRecord.php
--- a/src/infrastructure/edges/util/PhabricatorEdgeChangeRecord.php
+++ b/src/infrastructure/edges/util/PhabricatorEdgeChangeRecord.php
@@ -44,10 +44,18 @@
     return array_keys($rem);
   }
 
+  public function getModernOldEdgeTransactionData() {
+    return $this->getRemovedPHIDs();
+  }
+
+  public function getModernNewEdgeTransactionData() {
+    return $this->getAddedPHIDs();
+  }
+
   private function getOldDestinationPHIDs() {
     if ($this->xaction) {
       $old = $this->xaction->getOldValue();
-      return ipull($old, 'dst');
+      return $this->getPHIDsFromTransactionValue($old);
     }
 
     throw new Exception(
@@ -57,12 +65,27 @@
   private function getNewDestinationPHIDs() {
     if ($this->xaction) {
       $new = $this->xaction->getNewValue();
-      return ipull($new, 'dst');
+      return $this->getPHIDsFromTransactionValue($new);
     }
 
     throw new Exception(
       pht('Edge change record is not configured with any change data.'));
   }
 
+  private function getPHIDsFromTransactionValue($value) {
+    if (!$value) {
+      return array();
+    }
+
+    // If the list items are arrays, this is an older-style map of
+    // dictionaries.
+    $head = head($value);
+    if (is_array($head)) {
+      return ipull($value, 'dst');
+    }
+
+    // If the list items are not arrays, this is a newer-style list of PHIDs.
+    return $value;
+  }
 
 }