diff --git a/src/applications/diffusion/engineextension/DiffusionHovercardEngineExtension.php b/src/applications/diffusion/engineextension/DiffusionHovercardEngineExtension.php
--- a/src/applications/diffusion/engineextension/DiffusionHovercardEngineExtension.php
+++ b/src/applications/diffusion/engineextension/DiffusionHovercardEngineExtension.php
@@ -48,7 +48,20 @@
     $handles = $viewer->loadHandles($phids);
 
     $hovercard->setTitle($handle->getName());
-    $hovercard->setDetail($commit->getSummary());
+
+    // See T13620. Use a longer slice of the message than the "summary" here,
+    // since we have at least a few lines of room in the UI.
+    $commit_message = $commit->getCommitMessageForDisplay();
+
+    $message_limit = 512;
+
+    $short_message = id(new PhutilUTF8StringTruncator())
+      ->setMaximumBytes($message_limit * 4)
+      ->setMaximumGlyphs($message_limit)
+      ->truncateString($commit_message);
+    $short_message = phutil_escape_html_newlines($short_message);
+
+    $hovercard->setDetail($short_message);
 
     $repository = $handles[$repository_phid]->renderLink();
     $hovercard->addField(pht('Repository'), $repository);
@@ -64,7 +77,7 @@
     }
 
     $date = phabricator_date($commit->getEpoch(), $viewer);
-    $hovercard->addField(pht('Date'), $date);
+    $hovercard->addField(pht('Commit Date'), $date);
 
     if (!$commit->isAuditStatusNoAudit()) {
       $status = $commit->getAuditStatusObject();
diff --git a/src/applications/repository/storage/PhabricatorRepositoryCommit.php b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
--- a/src/applications/repository/storage/PhabricatorRepositoryCommit.php
+++ b/src/applications/repository/storage/PhabricatorRepositoryCommit.php
@@ -528,6 +528,12 @@
     return $data->getCommitterString();
   }
 
+  public function getCommitMessageForDisplay() {
+    $data = $this->getCommitData();
+    $message = $data->getCommitMessage();
+    return $message;
+  }
+
   public function newCommitRef(PhabricatorUser $viewer) {
     $repository = $this->getRepository();
 
diff --git a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
--- a/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
+++ b/src/applications/transactions/storage/PhabricatorApplicationTransaction.php
@@ -408,7 +408,7 @@
 
   public function renderHandleLink($phid) {
     if ($this->renderingTarget == self::TARGET_HTML) {
-      return $this->getHandle($phid)->renderLink();
+      return $this->getHandle($phid)->renderHovercardLink();
     } else {
       return $this->getHandle($phid)->getLinkName();
     }