--- a/mobile/android/base/java/org/mozilla/gecko/telemetry/pingbuilders/TelemetrySyncPingBundleBuilder.java
+++ b/mobile/android/base/java/org/mozilla/gecko/telemetry/pingbuilders/TelemetrySyncPingBundleBuilder.java
@@ -23,29 +23,32 @@ import java.util.Date;
 import java.util.List;
 import java.util.Locale;
 import java.util.TimeZone;
 
 /**
  * Responsible for building a Sync Ping, based on the telemetry docs:
  * https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/telemetry/data/sync-ping.html
  *
+ * Fields common to all pings are documented here:
+ * https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/telemetry/data/common-ping.html
+ *
  * This builder takes two stores ('sync' and 'event') and produces a single "sync ping".
  *
  * Note that until Bug 1363924, event telemetry will be ignored.
  *
  * Sample result will look something like:
  * {
  *     "syncs": [list of syncs, as produced by the SyncBuilder],
  *     "events": [list of events, as produced by the EventBuilder]
  * }
  */
 public class TelemetrySyncPingBundleBuilder extends TelemetryPingBuilder {
     private static final String PING_TYPE = "sync";
-    private static final int PING_BUNDLE_VERSION = 5; // Bug 1374758
+    private static final int PING_BUNDLE_VERSION = 4; // Bug 1410145
     private static final int PING_SYNC_DATA_FORMAT_VERSION = 1; // Bug 1374758
 
     public static final String UPLOAD_REASON_FIRST = "first";
     public static final String UPLOAD_REASON_CLOCK_DRIFT = "clockdrift";
     public static final String UPLOAD_REASON_SCHEDULE = "schedule";
     public static final String UPLOAD_REASON_IDCHANGE = "idchange";
     public static final String UPLOAD_REASON_COUNT = "count";
 

--- a/mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/pingbuilders/TelemetrySyncPingBundleBuilderTest.java
+++ b/mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/pingbuilders/TelemetrySyncPingBundleBuilderTest.java
@@ -107,17 +107,17 @@ public class TelemetrySyncPingBundleBuil
         builder.setSyncEventStore(eventPings);
 
         TelemetryOutgoingPing outgoingPing = builder.build();
 
         assertTrue(outgoingPing.getPayload().containsKey("application"));
         assertTrue(outgoingPing.getPayload().containsKey("payload"));
         assertTrue(outgoingPing.getPayload().containsKey("id"));
         assertEquals("sync", outgoingPing.getPayload().getString("type"));
-        assertEquals(Integer.valueOf(5), outgoingPing.getPayload().getIntegerSafely("version"));
+        assertEquals(Integer.valueOf(4), outgoingPing.getPayload().getIntegerSafely("version"));
 
         // Test application key.
         ExtendedJSONObject application = outgoingPing.getPayload().getObject("application");
         assertEquals("Mozilla", application.getString("vendor"));
         assertTrue(application.containsKey("architecture"));
         assertTrue(application.containsKey("platformVersion"));
         assertTrue(application.containsKey("displayVersion"));
         assertTrue(application.containsKey("version"));