diff --git a/printrun/gcoder.py b/printrun/gcoder.py
index ef5fd0a83..1a3fdaff5 100755
--- a/printrun/gcoder.py
+++ b/printrun/gcoder.py
@@ -240,6 +240,8 @@ def prepare(self, data = None, home_pos = None, layer_callback = None):
             self.layer_idxs = array('I', [])
             self.line_idxs = array('I', [])
 
+    def has_index(self, i):
+        return i < len(self)
     def __len__(self):
         return len(self.line_idxs)
 
diff --git a/printrun/printcore.py b/printrun/printcore.py
index beb9102d3..a4a545ac8 100644
--- a/printrun/printcore.py
+++ b/printrun/printcore.py
@@ -586,7 +586,7 @@ def _sendnext(self):
             self._send(self.priqueue.get_nowait())
             self.priqueue.task_done()
             return
-        if self.printing and self.queueindex < len(self.mainqueue):
+        if self.printing and self.mainqueue.has_index(self.queueindex):
             (layer, line) = self.mainqueue.idxs(self.queueindex)
             gline = self.mainqueue.all_layers[layer][line]
             if self.queueindex > 0:
@@ -604,7 +604,7 @@ def _sendnext(self):
                 try: handler.on_preprintsend(gline, self.queueindex, self.mainqueue)
                 except: logging.error(traceback.format_exc())
             if self.preprintsendcb:
-                if self.queueindex + 1 < len(self.mainqueue):
+                if self.mainqueue.has_index(self.queueindex + 1):
                     (next_layer, next_line) = self.mainqueue.idxs(self.queueindex + 1)
                     next_gline = self.mainqueue.all_layers[next_layer][next_line]
                 else:
diff --git a/printrun/pronsole.py b/printrun/pronsole.py
index 9aecc277f..60218b390 100644
--- a/printrun/pronsole.py
+++ b/printrun/pronsole.py
@@ -104,6 +104,37 @@ def bed_enabled(self):
     def extruder_enabled(self):
         return self.extruder_temp != 0
 
+class RGSGCoder():
+    """Bare alternative to gcoder.LightGCode which does not preload all lines in memory,
+but still allows run_gcode_script (hence the RGS) to be processed by do_print (checksum,threading,ok waiting)"""
+    def __init__(self, line):
+        self.lines = True
+        self.filament_length = 0.
+        self.filament_length_multi = [0]
+        self.proc = run_command(line, {"$s": 'str(self.filename)'}, stdout = subprocess.PIPE, universal_newlines = True)
+        lr = gcoder.Layer([])
+        lr.duration = 0.
+        self.all_layers = [lr]
+        self.read() #empty layer causes division by zero during progress calculation
+    def read(self):
+        ln = self.proc.stdout.readline()
+        if not ln:
+            self.proc.stdout.close()
+            return None
+        ln = ln.strip()
+        if not ln:
+            return None
+        pyLn = gcoder.PyLightLine(ln)
+        self.all_layers[0].append(pyLn)
+        return pyLn
+    def has_index(self, i):
+        while i >= len(self.all_layers[0]) and not self.proc.stdout.closed:
+            self.read()
+        return i < len(self.all_layers[0])
+    def __len__(self):
+        return len(self.all_layers[0])
+    def idxs(self, i):
+        return 0, i #layer, line
 
 class pronsole(cmd.Cmd):
     def __init__(self):
@@ -1755,9 +1786,11 @@ def help_run_script(self):
         self.log(_("Runs a custom script. Current gcode filename can be given using $s token."))
 
     def do_run_gcode_script(self, l):
-        p = run_command(l, {"$s": str(self.filename)}, stdout = subprocess.PIPE, universal_newlines = True)
-        for line in p.stdout.readlines():
-            self.onecmd(line.strip())
+        try:
+            self.fgcode = RGSGCoder(l)
+            self.do_print(None)
+        except BaseException as e:
+            self.logError(traceback.format_exc())
 
     def help_run_gcode_script(self):
         self.log(_("Runs a custom script which output gcode which will in turn be executed. Current gcode filename can be given using $s token."))
diff --git a/testtools/lengthy.py b/testtools/lengthy.py
new file mode 100755
index 000000000..c50bdb2af
--- /dev/null
+++ b/testtools/lengthy.py
@@ -0,0 +1,9 @@
+#!/usr/bin/python3
+#generate many g1 to test serial buffer overflow in run_gcode_script
+
+print('G28 X')
+print('G1 X0')
+for x in range(100):
+    print()
+    print('  ')
+    print('G1 X', x)