diff --git a/tools/tools-common.c b/tools/tools-common.c
index 210db52..7a7e897 100644
--- a/tools/tools-common.c
+++ b/tools/tools-common.c
@@ -146,7 +146,7 @@ print_keys_modmaps(struct xkb_keymap *keymap) {
 #endif
 
 void
-tools_print_keycode_state(char *prefix,
+tools_print_keycode_state(const char *prefix,
                           struct xkb_state *state,
                           struct xkb_compose_state *compose_state,
                           xkb_keycode_t keycode,
diff --git a/tools/tools-common.h b/tools/tools-common.h
index 1ff6c5a..33fa0e7 100644
--- a/tools/tools-common.h
+++ b/tools/tools-common.h
@@ -61,7 +61,7 @@ print_keys_modmaps(struct xkb_keymap *keymap);
 #endif
 
 void
-tools_print_keycode_state(char *prefix,
+tools_print_keycode_state(const char *prefix,
                           struct xkb_state *state,
                           struct xkb_compose_state *compose_state,
                           xkb_keycode_t keycode,