diff --git a/LuaLibs/ProcessLapJoint.lua b/LuaLibs/ProcessLapJoint.lua
index 579349a..9b4c6f1 100644
--- a/LuaLibs/ProcessLapJoint.lua
+++ b/LuaLibs/ProcessLapJoint.lua
@@ -6496,7 +6496,10 @@ local function MakeMoreFaces( Proc, nPhase, nRawId, nPartId, dOvmHead, bSinglePa
                      nSurfPartId = EgtSurfTmBySewing( nAddGrpId, { nSurfPartId, nTailCutId}, false)
                      EgtErase( nSurfPartIdOld)
                   end
-                  dCustomMaxElev = EgtSurfTmFacetElevationInClosedSurfTm( Proc.Id, nFacInd, nSurfPartId, true) + dCollSic
+                  dCustomMaxElev = EgtSurfTmFacetElevationInClosedSurfTm( Proc.Id, nFacInd, nSurfPartId, true)
+                  if dCustomMaxElev then
+                     dCustomMaxElev = dCustomMaxElev + dCollSic
+                  end
                   EgtErase( nSurfPartId)
                end
             end