diff --git a/printrun/printcore.py b/printrun/printcore.py
index b51d9e9bb..38282416d 100644
--- a/printrun/printcore.py
+++ b/printrun/printcore.py
@@ -250,7 +250,7 @@ def reset(self):
     def _readline(self):
         try:
             try:
-                line = self.printer.readline()
+                line = self.printer.readline().decode('ascii')
                 if self.printer_tcp and not line:
                     raise OSError(-1, "Read EOF from socket")
             except socket.timeout:
@@ -658,7 +658,7 @@ def _send(self, command, lineno = 0, calcchecksum = False):
                 try: self.sendcb(command, gline)
                 except: self.logError(traceback.format_exc())
             try:
-                self.printer.write(str(command + "\n"))
+                self.printer.write((command + "\n").encode('ascii'))
                 if self.printer_tcp:
                     try:
                         self.printer.flush()