diff --git a/wled00/FX_fcn.cpp b/wled00/FX_fcn.cpp
index 930f1f347..a71d8fdf9 100644
--- a/wled00/FX_fcn.cpp
+++ b/wled00/FX_fcn.cpp
@@ -587,7 +587,7 @@ void Segment::setMode(uint8_t fx, bool loadDefaults) {
         sOpt = extractModeDefaults(fx, "o1");   check1    = (sOpt >= 0) ? (bool)sOpt : false;
         sOpt = extractModeDefaults(fx, "o2");   check2    = (sOpt >= 0) ? (bool)sOpt : false;
         sOpt = extractModeDefaults(fx, "o3");   check3    = (sOpt >= 0) ? (bool)sOpt : false;
-        sOpt = extractModeDefaults(fx, "m12");  if (sOpt >= 0) map1D2D   = constrain(sOpt, 0, 7);
+        sOpt = extractModeDefaults(fx, "m12");  if (sOpt >= 0) map1D2D   = constrain(sOpt, 0, 7); else map1D2D = M12_Pixels;  // reset mapping if not defined (2D FX may not work)
         sOpt = extractModeDefaults(fx, "si");   if (sOpt >= 0) soundSim  = constrain(sOpt, 0, 1);
         sOpt = extractModeDefaults(fx, "rev");  if (sOpt >= 0) reverse   = (bool)sOpt;
         sOpt = extractModeDefaults(fx, "mi");   if (sOpt >= 0) mirror    = (bool)sOpt; // NOTE: setting this option is a risky business
@@ -1211,6 +1211,7 @@ void WS2812FX::service() {
           Segment::tmpsegd_t _tmpSegData;
           Segment::modeBlend(true);           // set semaphore
           seg.swapSegenv(_tmpSegData);        // temporarily store new mode state (and swap it with transitional state)
+          _virtualSegmentLength = seg.virtualLength(); // update SEGLEN (mapping may have changed)
           uint16_t d2 = (*_mode[tmpMode])();  // run old mode
           seg.restoreSegenv(_tmpSegData);     // restore mode state (will also update transitional state)
           delay = MIN(delay,d2);              // use shortest delay