diff --git a/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java b/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
index ef157d6a10..ebec9c59df 100644
--- a/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
+++ b/java/com/google/gerrit/server/notedb/rebuild/NoteDbMigrator.java
@@ -142,7 +142,7 @@ public class NoteDbMigrator implements AutoCloseable {
         logger.atInfo().log(outputBuffer.toString());
         outputBuffer = new StringBuilder();
       } else {
-        outputBuffer.append(b);
+        outputBuffer.append(Character.toChars(b));
       }
     }
   }