2 files changed, 5 insertions, 5 deletions
diff --git a/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java b/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
index bfefb94a7..f7890f814 100644
--- a/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
+++ b/src/main/java/org/traccar/protocol/Jt600FrameDecoder.java
@@ -35,7 +35,7 @@ public class Jt600FrameDecoder extends BaseFrameDecoder {
         char type = (char) buf.getByte(buf.readerIndex());
 
         if (type == '$') {
-            boolean longFormat = Jt600ProtocolDecoder.isLongFormat(buf, buf.readerIndex() + 1);
+            boolean longFormat = Jt600ProtocolDecoder.isLongFormat(buf);
             int length = buf.getUnsignedShort(buf.readerIndex() + (longFormat ? 8 : 7)) + 10;
             if (length <= buf.readableBytes()) {
                 return buf.readRetainedSlice(length);
diff --git a/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java b/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
index 9ed44f565..dc763dea7 100644
--- a/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
+++ b/src/main/java/org/traccar/protocol/Jt600ProtocolDecoder.java
@@ -86,8 +86,8 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
 
     }
 
-    static boolean isLongFormat(ByteBuf buf, int flagIndex) {
-        return buf.getUnsignedByte(flagIndex) >> 4 >= 7;
+    static boolean isLongFormat(ByteBuf buf) {
+        return buf.getUnsignedByte(buf.readerIndex() + 8) == 0;
     }
 
     static void decodeBinaryLocation(ByteBuf buf, Position position) {
@@ -123,9 +123,9 @@ public class Jt600ProtocolDecoder extends BaseProtocolDecoder {
 
         List<Position> positions = new LinkedList<>();
 
-        buf.readByte(); // header
+        boolean longFormat = isLongFormat(buf);
 
-        boolean longFormat = isLongFormat(buf, buf.readerIndex());
+        buf.readByte(); // header
 
         String id = String.valueOf(Long.parseLong(ByteBufUtil.hexDump(buf.readSlice(5))));
         DeviceSession deviceSession = getDeviceSession(channel, remoteAddress, id);