diff --git a/firmware/src/main.c b/firmware/src/main.c
index 37d994f..44d33da 100644
--- a/firmware/src/main.c
+++ b/firmware/src/main.c
@@ -88,7 +88,8 @@ static const __flash uint8_t sym_t[] = { 0x0C, 0x0C, 0xFC, 0xFC, 0x0C, 0x0C,
 static const __flash uint8_t sym_u[] = { 0xFC, 0xFC, 0x00, 0x00, 0xFC, 0xFC,
                                          0x3F, 0x3F, 0x30, 0x30, 0x3F, 0x3F };
 
-static const __flash uint8_t sym_none[] = { 0x00 };
+static const __flash uint8_t sym_invalid[] = { 0x80, 0xE0, 0x98, 0xCC, 0x4C, 0x18, 0xE0, 0x80,
+                                               0x01, 0x07, 0x1F, 0x24, 0x25, 0x1F, 0x07, 0x01};
 
 struct symbol {
     const __flash uint8_t* data;
@@ -106,29 +107,29 @@ static const struct symbol symbol_table[] = { SYM_ENTRY(sym_0),
                                               SYM_ENTRY(sym_8),
                                               SYM_ENTRY(sym_9),
                                               SYM_ENTRY(sym_colon),
-                                              SYM_ENTRY(sym_none),
-                                              SYM_ENTRY(sym_none),
-                                              SYM_ENTRY(sym_none),
-                                              SYM_ENTRY(sym_none),
-                                              SYM_ENTRY(sym_none),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
+                                              SYM_ENTRY(sym_invalid),
+                                              SYM_ENTRY(sym_invalid),
+                                              SYM_ENTRY(sym_invalid),
+                                              SYM_ENTRY(sym_invalid),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_a),
                                               SYM_ENTRY(sym_b),
                                               SYM_ENTRY(sym_c),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_e),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_g),
                                               SYM_ENTRY(sym_h),
                                               SYM_ENTRY(sym_i),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_k),
                                               SYM_ENTRY(sym_l),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_n),
                                               SYM_ENTRY(sym_o),
                                               SYM_ENTRY(sym_p),
-                                              SYM_ENTRY(sym_none),
+                                              SYM_ENTRY(sym_invalid),
                                               SYM_ENTRY(sym_r),
                                               SYM_ENTRY(sym_s),
                                               SYM_ENTRY(sym_t),