diff --git a/lib/KOReaderSync/KOReaderSyncClient.cpp b/lib/KOReaderSync/KOReaderSyncClient.cpp
index 4df5e225..1e60c4c0 100644
--- a/lib/KOReaderSync/KOReaderSyncClient.cpp
+++ b/lib/KOReaderSync/KOReaderSyncClient.cpp
@@ -520,7 +520,9 @@ KOReaderSyncClient::Error KOReaderSyncClient::getProgress(const std::string& doc
     // HTTP 200 with an empty body ("{}"), not by 404. Detect that here so the
     // caller doesn't apply a zeroed-out position as if it were real progress.
     if (doc["document"].isNull() || doc["progress"].isNull()) {
-      LOG_DBG("KOSync", "Empty progress payload — treating as not found");
+      std::string jsonDump;
+      serializeJson(doc, jsonDump);
+      LOG_DBG("KOSync", "Empty progress payload — treating as not found | payload=%s", jsonDump.c_str());
       return NOT_FOUND;
     }