diff --git a/DCC.cpp b/DCC.cpp
index e81cb04..6942d76 100644
--- a/DCC.cpp
+++ b/DCC.cpp
@@ -523,6 +523,7 @@ const ackOp FLASH LOCO_ID_PROG[] = {
       V0, WACK, MERGE,
       V0, WACK, MERGE,
       VB, WACK, NAKSKIP, // bad read of cv20, assume its 0 
+      BAD20SKIP,     // detect invalid cv20 value and ignore 
       STASHLOCOID,   // keep cv 20 until we have cv19 as well.
       SETCV, (ackOp)19, 
       STARTMERGE,           // Setup to read cv 19
@@ -628,7 +629,9 @@ const ackOp FLASH CONSIST_ID_PROG[] = {
       BASELINE,
       SETCV,(ackOp)20,
       SETBYTEH,    // high byte to CV 20
-      WB,WACK,     // ignore dedcoder without cv20 support
+      WB,WACK,ITSKIP,
+      FAIL_IF_NONZERO_NAK, // fail if writing long address to decoder that cant support it
+      SKIPTARGET,
       SETCV,(ackOp)19,
       SETBYTEL,   // low byte of word
       WB,WACK,ITC1,   // If ACK, we are done - callback(1) means Ok
diff --git a/DCCACK.cpp b/DCCACK.cpp
index 7a43cd1..0ae5224 100644
--- a/DCCACK.cpp
+++ b/DCCACK.cpp
@@ -347,6 +347,20 @@ void DCCACK::loop() {
             opcode=GETFLASH(ackManagerProg);
           }
           break;
+     case BAD20SKIP:
+          if (ackManagerByte > 120) {
+            // skip to SKIPTARGET if cv20 is >120 (some decoders respond with 255)
+            if (Diag::ACK) DIAG(F("XX cv20=%d "),ackManagerByte);
+            while (opcode!=SKIPTARGET) {
+              ackManagerProg++;
+              opcode=GETFLASH(ackManagerProg);
+            }
+          }
+          break; 
+     case FAIL_IF_NONZERO_NAK: // fail if writing long address to decoder that cant support it
+          if (ackManagerByte==0) break;
+          callback(-4);  
+          return;           
      case SKIPTARGET:
           break;
      default:
diff --git a/DCCACK.h b/DCCACK.h
index c50dbbd..3a6148d 100644
--- a/DCCACK.h
+++ b/DCCACK.h
@@ -58,6 +58,8 @@ enum ackOp : byte
   ITSKIP,           // skip to SKIPTARGET if ack true
   NAKSKIP,          // skip to SKIPTARGET if ack false
   COMBINE1920,      // combine cvs 19 and 20 and callback
+  BAD20SKIP,        // skip to SKIPTARGET if cv20 is >120 (some decoders respond with 255) 
+  FAIL_IF_NONZERO_NAK, // fail if writing long address to decoder that cant support it
   SKIPTARGET = 0xFF // jump to target
 };
 
diff --git a/DCCEXParser.cpp b/DCCEXParser.cpp
index 6bec5fb..0aae191 100644
--- a/DCCEXParser.cpp
+++ b/DCCEXParser.cpp
@@ -1452,6 +1452,7 @@ void DCCEXParser::callback_Wloco(int16_t result)
 
 void DCCEXParser::callback_Wconsist(int16_t result)
 {
+    if (result==-4) DIAG(F("Long Consist %d not supported by decoder"),stashP[1]);
     if (result==1) result=stashP[1]; // pick up original requested id from command
     StringFormatter::send(getAsyncReplyStream(), F("<w CONSIST %d%S>\n"),
      result, stashP[2]=="REVERSE"_hk ? F(" REVERSE") : F(""));
diff --git a/version.h b/version.h
index ccf326c..131d09a 100644
--- a/version.h
+++ b/version.h
@@ -3,7 +3,9 @@
 
 #include "StringFormatter.h"
 
-#define VERSION "5.4.8"
+#define VERSION "5.4.9"
+// 5.4.9  - Handle non-compliant decoders returning 255 for cv 20 and confusing <R> with bad consist addresses.
+//        - <W CONSIST longaddr> handles non-compliant decoders which NAK cv 20 writes.
 // 5.4.8  - Bugfix: Insert idle packet at end of speed reminder loop; treat all function groups equal
 // 5.4.7  - Bugfix: EXRAIL fix CLEAR_ALL_STASH
 // 5.4.6  - Bugfix: Do not drop further commands in same packet