diff --git a/server/src/hardware/protocol/z21/clientkernel.cpp b/server/src/hardware/protocol/z21/clientkernel.cpp
index b032be92..4f78a39d 100644
--- a/server/src/hardware/protocol/z21/clientkernel.cpp
+++ b/server/src/hardware/protocol/z21/clientkernel.cpp
@@ -121,10 +121,11 @@ void ClientKernel::receive(const Message& message)
           {
             const auto& reply = static_cast<const LanXLocoInfo&>(message);
 
-            const int maxFunc = reply.supportsF29F31() ? 31 : 28;
-            bool val[31 + 1] = {};
+            //NOTE: there is also a function at index 0, hence +1
+            const int functionIndexMax = std::min(reply.functionIndexMax(), LanXLocoInfo::supportedFunctionIndexMax);
+            bool val[LanXLocoInfo::supportedFunctionIndexMax + 1] = {};
 
-            for(int i = 0; i <= maxFunc; i++)
+            for(int i = 0; i <= functionIndexMax; i++)
             {
               val[i] = reply.getFunction(i);
             }
@@ -231,7 +232,7 @@ void ClientKernel::receive(const Message& message)
             EventLoop::call(
               [this, address=reply.address(), isEStop=reply.isEmergencyStop(),
               speed = reply.speedStep(), speedMax=reply.speedSteps(),
-              dir = reply.direction(), val, maxFunc, changes]()
+              dir = reply.direction(), val, functionIndexMax, changes]()
               {
                 try
                 {
@@ -262,7 +263,7 @@ void ClientKernel::receive(const Message& message)
 
                     //Function get always updated because we do not store a copy in cache
                     //so there is no way to tell in advance if they changed
-                    for(int i = 0; i <= maxFunc; i++)
+                    for(int i = 0; i <= functionIndexMax; i++)
                     {
                       decoder->setFunctionValue(i, val[i]);
                     }
diff --git a/server/src/hardware/protocol/z21/messages.cpp b/server/src/hardware/protocol/z21/messages.cpp
index 199c6b01..a3a8659c 100644
--- a/server/src/hardware/protocol/z21/messages.cpp
+++ b/server/src/hardware/protocol/z21/messages.cpp
@@ -195,7 +195,8 @@ std::string toString(const Message& message, bool raw)
             s.append("estop");
           else
             s.append(std::to_string(locoInfo.speedStep())).append("/").append(std::to_string(locoInfo.speedSteps()));
-          for(uint8_t i = 0; i <= LanXLocoInfo::functionIndexMax; i++)
+          const uint8_t functionIndexMax = locoInfo.functionIndexMax();
+          for(uint8_t i = 0; i <= functionIndexMax; i++)
             s.append(" f").append(std::to_string(i)).append("=").append(locoInfo.getFunction(i) ? "1" : "0");
           s.append(" busy=").append(locoInfo.isBusy() ? "1" : "0");
           break;
diff --git a/server/src/hardware/protocol/z21/messages.hpp b/server/src/hardware/protocol/z21/messages.hpp
index cd6635f5..d7f57c56 100644
--- a/server/src/hardware/protocol/z21/messages.hpp
+++ b/server/src/hardware/protocol/z21/messages.hpp
@@ -1121,7 +1121,7 @@ struct LanXLocoInfo : LanX
   static constexpr uint8_t directionFlag = 0x80;
   static constexpr uint8_t speedStepMask = 0x7F;
   static constexpr uint8_t flagF0 = 0x10;
-  static constexpr uint8_t functionIndexMax = 28;
+  static constexpr uint8_t supportedFunctionIndexMax = 31; ///< \sa functionIndexMax
 
   static constexpr uint8_t minMessageSize = 7 + 7;
   static constexpr uint8_t maxMessageSize = 7 + 14;
@@ -1131,11 +1131,11 @@ struct LanXLocoInfo : LanX
   uint8_t db2 = 0;
   uint8_t speedAndDirection = 0; //db3
   uint8_t db4 = 0;
-  uint8_t f5f12 = 0;    //db5
-  uint8_t f13f20 = 0;   //db6
-  uint8_t f21f28 = 0;   //db7
-  uint8_t f29f31 = 0;   //db8 (firmware >= 1.42)
-  uint8_t checksum = 0;
+  uint8_t f5f12 = 0;  //db5
+  uint8_t f13f20 = 0; //db6
+  uint8_t f21f28 = 0; //db7
+  uint8_t db8 = 0;    //db8 is f29f31 (firmware >= 1.42) otherwise checksum
+  uint8_t db9 = 0;    //checksum (firmware >= 1.42)
 
   LanXLocoInfo() :
     LanX(sizeof(LanXLocoInfo), LAN_X_LOCO_INFO)
@@ -1233,6 +1233,28 @@ struct LanXLocoInfo : LanX
     return dataLen() >= 15;
   }
 
+  /*!
+   * \brief Get maximum fuction index stored in this message
+   * \return Maximum index
+   *
+   * \note There is also a function at index 0 so count it
+   *
+   * Maximum function index depends on Z21 firmware protocol version
+   * versions <  1.42 support up to F28
+   * versions >= 1.42 support up to F31
+   *
+   * Messages are backward compatible but older version will only read
+   * up to their maximum function number
+   *
+   * We currently support up to F31 in trasmission and reception \sa supportedFunctionIndexMax
+   */
+  inline uint8_t functionIndexMax() const
+  {
+    if(supportsF29F31())
+      return 31;
+    return 28;
+  }
+
   bool getFunction(uint8_t index) const
   {
     if(index == 0)
@@ -1246,7 +1268,7 @@ struct LanXLocoInfo : LanX
     else if(index <= 28)
       return f21f28 & (1 << (index - 21));
     else if(index <= 31 && supportsF29F31())
-      return f29f31 & (1 << (index - 29));
+      return db8 & (1 << (index - 29));
     else
       return false;
   }
@@ -1296,9 +1318,9 @@ struct LanXLocoInfo : LanX
     {
       const uint8_t flag = (1 << (index - 29));
       if(value)
-        f29f31 |= flag;
+        db8 |= flag;
       else
-        f29f31 &= ~flag;
+        db8 &= ~flag;
     }
   }