diff --git a/src/Mod/Path/PathScripts/post/smoothie_post.py b/src/Mod/Path/PathScripts/post/smoothie_post.py
index 6fcc907176..6929f1ba39 100644
--- a/src/Mod/Path/PathScripts/post/smoothie_post.py
+++ b/src/Mod/Path/PathScripts/post/smoothie_post.py
@@ -266,7 +266,7 @@ def sendToSmoothie(IP_ADDR, GCODE, fname):
     s =  socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     s.settimeout(4.0)
     s.connect((IP_ADDR, 115))
-    tn= s.makefile()
+    tn= s.makefile(mode='rw')
 
 # read startup prompt
     ln= tn.readline()