diff --git a/scripts/kconfig/nconf.c b/scripts/kconfig/nconf.c
index a9bc5334a478..003114779815 100644
--- a/scripts/kconfig/nconf.c
+++ b/scripts/kconfig/nconf.c
@@ -271,7 +271,7 @@ static struct mitem k_menu_items[MAX_MENU_ITEMS];
 static int items_num;
 static int global_exit;
 /* the currently selected button */
-const char *current_instructions = menu_instructions;
+static const char *current_instructions = menu_instructions;
 
 static char *dialog_input_result;
 static int dialog_input_result_len;
@@ -305,7 +305,7 @@ struct function_keys {
 };
 
 static const int function_keys_num = 9;
-struct function_keys function_keys[] = {
+static struct function_keys function_keys[] = {
 	{
 		.key_str = "F1",
 		.func = "Help",
@@ -508,7 +508,7 @@ static int get_mext_match(const char *match_str, match_f flag)
 	index = (index + items_num) % items_num;
 	while (true) {
 		char *str = k_menu_items[index].str;
-		if (strcasestr(str, match_str) != 0)
+		if (strcasestr(str, match_str) != NULL)
 			return index;
 		if (flag == FIND_NEXT_MATCH_UP ||
 		    flag == MATCH_TINKER_PATTERN_UP)
@@ -1067,7 +1067,7 @@ static int do_match(int key, struct match_state *state, int *ans)
 
 static void conf(struct menu *menu)
 {
-	struct menu *submenu = 0;
+	struct menu *submenu = NULL;
 	const char *prompt = menu_get_prompt(menu);
 	struct symbol *sym;
 	int res;
@@ -1234,7 +1234,7 @@ static void show_help(struct menu *menu)
 static void conf_choice(struct menu *menu)
 {
 	const char *prompt = _(menu_get_prompt(menu));
-	struct menu *child = 0;
+	struct menu *child = NULL;
 	struct symbol *active;
 	int selected_index = 0;
 	int last_top_row = 0;
@@ -1456,7 +1456,7 @@ static void conf_save(void)
 	}
 }
 
-void setup_windows(void)
+static void setup_windows(void)
 {
 	int lines, columns;
 
diff --git a/scripts/kconfig/nconf.gui.c b/scripts/kconfig/nconf.gui.c
index 4b2f44c20caf..a64b1c31253e 100644
--- a/scripts/kconfig/nconf.gui.c
+++ b/scripts/kconfig/nconf.gui.c
@@ -129,7 +129,7 @@ static void no_colors_theme(void)
 	mkattrn(FUNCTION_TEXT, A_REVERSE);
 }
 
-void set_colors()
+void set_colors(void)
 {
 	start_color();
 	use_default_colors();
@@ -192,7 +192,7 @@ const char *get_line(const char *text, int line_no)
 	int lines = 0;
 
 	if (!text)
-		return 0;
+		return NULL;
 
 	for (i = 0; text[i] != '\0' && lines < line_no; i++)
 		if (text[i] == '\n')