diff --git a/wled00/FX_fcn.cpp b/wled00/FX_fcn.cpp
index 235c61d0f..1688d737c 100644
--- a/wled00/FX_fcn.cpp
+++ b/wled00/FX_fcn.cpp
@@ -1611,7 +1611,7 @@ void WS2812FX::deserializeMap(uint8_t n) {
     customMappingSize  = map.size();
     customMappingTable = new uint16_t[customMappingSize];
     for (uint16_t i=0; i<customMappingSize; i++) {
-      customMappingTable[i] = (uint16_t) map[i];
+      customMappingTable[i] = (uint16_t) (map[i]<0 ? 0xFFFFU : map[i]);
     }
   }