diff --git a/scripts/buildcommands.py b/scripts/buildcommands.py
index a26801ee..0c147191 100644
--- a/scripts/buildcommands.py
+++ b/scripts/buildcommands.py
@@ -29,9 +29,6 @@ def error(msg):
 ######################################################################
 
 def build_parser(parser, iscmd, all_param_types):
-    if parser.name == "#empty":
-        return "\n    // Empty message\n    .max_size=%d," % (
-            msgproto.MESSAGE_MIN,)
     if parser.name == "#output":
         comment = "Output: " + parser.msgformat
     else:
@@ -71,8 +68,6 @@ def build_encoders(encoders, msg_to_id, all_param_types):
         if msgid in did_output:
             continue
         s = msg
-        if s == '#empty':
-            s = ''
         did_output[msgid] = True
         code = ('    if (__builtin_strcmp(str, "%s") == 0)\n'
                 '        return &command_encoder_%s;\n' % (s, msgid))
@@ -308,10 +303,7 @@ def main():
                 error("Conflicting definition for command '%s'" % msgname)
             messages_by_name[msgname] = msg
         elif cmd == '_DECL_ENCODER':
-            if len(parts) == 1:
-                msgname = msg = "#empty"
-            else:
-                msgname = parts[1]
+            msgname = parts[1]
             m = messages_by_name.get(msgname)
             if m is not None and m != msg:
                 error("Conflicting definition for message '%s'" % msgname)
diff --git a/src/command.c b/src/command.c
index 62db0bfd..af84539f 100644
--- a/src/command.c
+++ b/src/command.c
@@ -222,6 +222,11 @@ command_lookup_parser(uint8_t cmdid)
     return &command_index[cmdid];
 }
 
+// Empty message (for ack/nak transmission)
+const struct command_encoder encode_acknak PROGMEM = {
+    .max_size = MESSAGE_MIN,
+};
+
 enum { CF_NEED_SYNC=1<<0, CF_NEED_VALID=1<<1 };
 
 // Find the next complete message.
@@ -256,7 +261,7 @@ command_find_block(char *buf, uint8_t buf_len, uint8_t *pop_count)
         goto nak;
     }
     next_sequence = ((msgseq + 1) & MESSAGE_SEQ_MASK) | MESSAGE_DEST;
-    sendf(""); // An empty message with a new sequence number is an ack
+    command_sendf(&encode_acknak);
     return 1;
 
 need_more_data:
@@ -282,7 +287,7 @@ need_sync: ;
         return -1;
     sync_state |= CF_NEED_VALID;
 nak:
-    sendf(""); // An empty message with a duplicate sequence number is a nak
+    command_sendf(&encode_acknak);
     return -1;
 }