diff --git a/resources/sql/autopatches/20161213.diff.01.hunks.php b/resources/sql/autopatches/20161213.diff.01.hunks.php
index c6394defce..574adb3b4f 100644
--- a/resources/sql/autopatches/20161213.diff.01.hunks.php
+++ b/resources/sql/autopatches/20161213.diff.01.hunks.php
@@ -1,38 +1,39 @@
 <?php
 
 $conn = id(new DifferentialRevision())->establishConnection('w');
 $src_table = 'differential_hunk';
 $dst_table = 'differential_hunk_modern';
 
 echo tsprintf(
   "%s\n",
   pht('Migrating old hunks...'));
 
 foreach (new LiskRawMigrationIterator($conn, $src_table) as $row) {
   queryfx(
     $conn,
     'INSERT INTO %T
       (changesetID, oldOffset, oldLen, newOffset, newLen,
         dataType, dataEncoding, dataFormat, data,
         dateCreated, dateModified)
       VALUES
       (%d, %d, %d, %d, %d,
         %s, %s, %s, %s,
         %d, %d)',
     $dst_table,
     $row['changesetID'],
     $row['oldOffset'],
     $row['oldLen'],
     $row['newOffset'],
     $row['newLen'],
     DifferentialModernHunk::DATATYPE_TEXT,
     'utf8',
     DifferentialModernHunk::DATAFORMAT_RAW,
-    $row['changes'],
+    // In rare cases, this could be NULL. See T12090.
+    (string)$row['changes'],
     $row['dateCreated'],
     $row['dateModified']);
 }
 
 echo tsprintf(
   "%s\n",
   pht('Done.'));