diff --git a/reactor-plc/startup.lua b/reactor-plc/startup.lua
index 659c8a6..ae38449 100644
--- a/reactor-plc/startup.lua
+++ b/reactor-plc/startup.lua
@@ -12,7 +12,7 @@ os.loadAPI("config.lua")
 os.loadAPI("plc.lua")
 os.loadAPI("threads.lua")
 
-local R_PLC_VERSION = "alpha-v0.4.3"
+local R_PLC_VERSION = "alpha-v0.4.4"
 
 local print = util.print
 local println = util.println
diff --git a/reactor-plc/threads.lua b/reactor-plc/threads.lua
index ce17609..b774dbb 100644
--- a/reactor-plc/threads.lua
+++ b/reactor-plc/threads.lua
@@ -239,7 +239,7 @@ function thread__iss(smem)
             end
         
             -- check for messages in the message queue
-            while iss_queue.ready() do
+            while iss_queue.ready() and not plc_state.shutdown do
                 local msg = iss_queue.pop()
 
                 if msg.qtype == mqueue.TYPE.COMMAND then
@@ -331,7 +331,7 @@ function thread__comms(smem)
         -- thread loop
         while true do
             -- check for messages in the message queue
-            while comms_queue.ready() do
+            while comms_queue.ready() and not plc_state.shutdown do
                 local msg = comms_queue.pop()
 
                 if msg.qtype == mqueue.TYPE.COMMAND then
diff --git a/rtu/startup.lua b/rtu/startup.lua
index be27048..8fea859 100644
--- a/rtu/startup.lua
+++ b/rtu/startup.lua
@@ -19,7 +19,7 @@ os.loadAPI("dev/boiler_rtu.lua")
 os.loadAPI("dev/imatrix_rtu.lua")
 os.loadAPI("dev/turbine_rtu.lua")
 
-local RTU_VERSION = "alpha-v0.4.3"
+local RTU_VERSION = "alpha-v0.4.4"
 
 local print = util.print
 local println = util.println
diff --git a/rtu/threads.lua b/rtu/threads.lua
index 692697d..c8abdd9 100644
--- a/rtu/threads.lua
+++ b/rtu/threads.lua
@@ -121,7 +121,7 @@ function thread__comms(smem)
         -- thread loop
         while true do
             -- check for messages in the message queue
-            while comms_queue.ready() do
+            while comms_queue.ready() and not plc_state.shutdown do
                 local msg = comms_queue.pop()
 
                 if msg.qtype == mqueue.TYPE.COMMAND then