diff --git "a/irmp.c" "b/irmp.c"
index bbaca5a..f1b434e 100644
--- "a/irmp.c"
+++ "b/irmp.c"
@@ -5564,7 +5564,7 @@ printf ("fm: %d %d\n", irmp_pulse_time * 1000000 / F_INTERRUPTS, RCII_BIT_LEN *
  */
 
 void
-print_spectrum (char * text, int * buf, int is_pulse)
+print_spectrum (const char * text, int * buf, int is_pulse)
 {
     int     i;
     int     j;
@@ -5681,7 +5681,7 @@ print_spectrum (char * text, int * buf, int is_pulse)
 static uint_fast8_t
 get_fdc_key (uint_fast16_t cmd)
 {
-    static uint8_t key_table[128] =
+    static const uint8_t key_table[128] =
     {
      // 0     1    2    3    4    5    6    7    8     9     A     B     C     D    E    F
          0,   '^', '1', '2', '3', '4', '5', '6', '7',  '8',  '9',  '0',  0xDF, '´', 0,   '\b',
@@ -5821,7 +5821,7 @@ next_tick (void)
                 }
                 else if (key == '\r' || key == '\t' || key == KEY_ESCAPE || (key >= 0x80 && key <= 0x9F))                 // function keys
                 {
-                    char * p = (char *) NULL;
+                    const char * p = (const char *) NULL;
 
                     switch (key)
                     {