diff --git a/supervisor/startup.lua b/supervisor/startup.lua
index ff2ec5b..85a229e 100644
--- a/supervisor/startup.lua
+++ b/supervisor/startup.lua
@@ -22,7 +22,7 @@ local supervisor = require("supervisor.supervisor")
 
 local svsessions = require("supervisor.session.svsessions")
 
-local SUPERVISOR_VERSION = "v1.5.17"
+local SUPERVISOR_VERSION = "v1.5.18"
 
 local println = util.println
 local println_ts = util.println_ts
diff --git a/supervisor/unit.lua b/supervisor/unit.lua
index ebb4111..794b3bf 100644
--- a/supervisor/unit.lua
+++ b/supervisor/unit.lua
@@ -813,7 +813,7 @@ function unit.new(reactor_id, num_boilers, num_turbines, ext_idle)
         if limit > 0 then
             self.db.control.lim_br100 = math.floor(limit * 100)
 
-            if self.plc_i ~= nil then
+            if (self.plc_i ~= nil) and (type(self.plc_i.get_struct().max_burn) == "number") then
                 if limit > self.plc_i.get_struct().max_burn then
                     self.db.control.lim_br100 = math.floor(self.plc_i.get_struct().max_burn * 100)
                 end