diff --git a/klippy/mcu.py b/klippy/mcu.py
index f03fd16d..3f88c3e5 100644
--- a/klippy/mcu.py
+++ b/klippy/mcu.py
@@ -4,7 +4,7 @@
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import sys, os, zlib, logging, math
-import serialhdl, pins, chelper, clocksync
+import serialhdl, msgproto, pins, chelper, clocksync
 
 class error(Exception):
     pass
@@ -548,17 +548,26 @@ class MCU:
             raise error("MCU '%s' CRC does not match config" % (self._name,))
         # Transmit config messages (if needed)
         self.register_response(self._handle_starting, 'starting')
-        if prev_crc is None:
-            logging.info("Sending MCU '%s' printer configuration...",
-                         self._name)
-            for c in self._config_cmds:
+        try:
+            if prev_crc is None:
+                logging.info("Sending MCU '%s' printer configuration...",
+                             self._name)
+                for c in self._config_cmds:
+                    self._serial.send(c)
+            else:
+                for c in self._restart_cmds:
+                    self._serial.send(c)
+            # Transmit init messages
+            for c in self._init_cmds:
                 self._serial.send(c)
-        else:
-            for c in self._restart_cmds:
-                self._serial.send(c)
-        # Transmit init messages
-        for c in self._init_cmds:
-            self._serial.send(c)
+        except msgproto.enumeration_error as e:
+            enum_name, enum_value = e.get_enum_params()
+            if enum_name == 'pin':
+                # Raise pin name errors as a config error (not a protocol error)
+                raise self._printer.config_error(
+                    "Pin '%s' is not a valid pin name on mcu '%s'"
+                    % (enum_value, self._name))
+            raise
     def _send_get_config(self):
         get_config_cmd = self.lookup_query_command(
             "get_config",
diff --git a/klippy/msgproto.py b/klippy/msgproto.py
index cdecd8e7..7391a6f4 100644
--- a/klippy/msgproto.py
+++ b/klippy/msgproto.py
@@ -86,12 +86,14 @@ class PT_progmem_buffer(PT_string):
 class PT_buffer(PT_string):
     pass
 
-MessageTypes = {
-    '%u': PT_uint32(), '%i': PT_int32(),
-    '%hu': PT_uint16(), '%hi': PT_int16(),
-    '%c': PT_byte(),
-    '%s': PT_string(), '%.*s': PT_progmem_buffer(), '%*s': PT_buffer(),
-}
+class enumeration_error(error):
+    def __init__(self, enum_name, value):
+        self.enum_name = enum_name
+        self.value = value
+        error.__init__(self, "Unknown value '%s' in enumeration '%s'"
+                       % (value, enum_name))
+    def get_enum_params(self):
+        return self.enum_name, self.value
 
 class Enumeration:
     is_int = False
@@ -105,8 +107,7 @@ class Enumeration:
     def encode(self, out, v):
         tv = self.enums.get(v)
         if tv is None:
-            raise error("Unknown value '%s' in enumeration '%s'"
-                        % (v, self.enum_name))
+            raise enumeration_error(self.enum_name, v)
         self.pt.encode(out, tv)
     def parse(self, s, pos):
         v, pos = self.pt.parse(s, pos)
@@ -115,6 +116,13 @@ class Enumeration:
             tv = "?%d" % (v,)
         return tv, pos
 
+MessageTypes = {
+    '%u': PT_uint32(), '%i': PT_int32(),
+    '%hu': PT_uint16(), '%hi': PT_int16(),
+    '%c': PT_byte(),
+    '%s': PT_string(), '%.*s': PT_progmem_buffer(), '%*s': PT_buffer(),
+}
+
 # Lookup the message types for a format string
 def lookup_params(msgformat, enumerations={}):
     out = []