diff --git a/src/bfu/hierbox.c b/src/bfu/hierbox.c
index 751d4c574..399ff4d76 100644
--- a/src/bfu/hierbox.c
+++ b/src/bfu/hierbox.c
@@ -438,7 +438,7 @@ push_hierbox_info_button(struct dialog_data *dlg_data, struct widget_data *butto
 		N_("Info"), ALIGN_LEFT,
 		msg,
 		context, 1,
-		N_("~OK"), done_listbox_context, B_ESC | B_ENTER);
+		MSG_BOX_BUTTON(N_("~OK"), done_listbox_context, B_ESC | B_ENTER));
 
 	return EVENT_PROCESSED;
 }
@@ -751,8 +751,8 @@ query_delete_selected_item(void *context_)
 			listbox_message(delete_folder_title), ALIGN_CENTER,
 			msg_text(term, listbox_message(delete_folder), text),
 			context, 2,
-			N_("~Yes"), push_ok_delete_button, B_ENTER,
-			N_("~No"), done_listbox_context, B_ESC);
+			MSG_BOX_BUTTON(N_("~Yes"), push_ok_delete_button, B_ENTER),
+			MSG_BOX_BUTTON(N_("~No"), done_listbox_context, B_ESC));
 	} else {
 		unsigned char *msg = ops->get_info(item, term);
 
@@ -763,8 +763,8 @@ query_delete_selected_item(void *context_)
 			msg_text(term, listbox_message(delete_item),
 			         text, empty_string_or_(msg)),
 			context, 2,
-			N_("~Yes"), push_ok_delete_button, B_ENTER,
-			N_("~No"), done_listbox_context, B_ESC);
+			MSG_BOX_BUTTON(N_("~Yes"), push_ok_delete_button, B_ENTER),
+			MSG_BOX_BUTTON(N_("~No"), done_listbox_context, B_ESC));
 		mem_free_if(msg);
 	}
 	mem_free(text);
@@ -772,6 +772,12 @@ query_delete_selected_item(void *context_)
 	return EVENT_PROCESSED;
 }
 
+static void
+dont_delete_marked_items(void *const context_)
+{
+	query_delete_selected_item(context_);
+}
+
 widget_handler_status_T
 push_hierbox_delete_button(struct dialog_data *dlg_data,
 			   struct widget_data *button)
@@ -805,8 +811,8 @@ push_hierbox_delete_button(struct dialog_data *dlg_data,
 		listbox_message(delete_marked_items_title), ALIGN_CENTER,
 		listbox_message(delete_marked_items),
 		context, 2,
-		N_("~Yes"), push_ok_delete_button, B_ENTER,
-		N_("~No"), query_delete_selected_item, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), push_ok_delete_button, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), dont_delete_marked_items, B_ESC));
 
 	return EVENT_PROCESSED;
 }
@@ -867,8 +873,8 @@ push_hierbox_clear_button(struct dialog_data *dlg_data,
 		listbox_message(clear_all_items_title), ALIGN_CENTER,
 		listbox_message(clear_all_items),
 		context, 2,
-		N_("~Yes"), do_clear_browser, B_ENTER,
-		N_("~No"), NULL, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), do_clear_browser, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), NULL, B_ESC));
 
 	return EVENT_PROCESSED;
 }
diff --git a/src/bfu/msgbox.c b/src/bfu/msgbox.c
index 00924cbd0..d7af62be5 100644
--- a/src/bfu/msgbox.c
+++ b/src/bfu/msgbox.c
@@ -71,7 +71,7 @@ msg_box(struct terminal *term, struct memory_list *ml, enum msgbox_flags flags,
 		int bflags;
 
 		label = va_arg(ap, unsigned char *);
-		done = va_arg(ap, void *);
+		done = va_arg(ap, done_handler_T *);
 		bflags = va_arg(ap, int);
 
 		if (!label) {
@@ -170,7 +170,7 @@ refreshed_msg_box(struct terminal *term, enum msgbox_flags flags,
 			   title, align,
 			   info,
 			   data, 1,
-			   N_("~OK"), NULL, B_ENTER | B_ESC);
+			   MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC));
 
 	if (!dlg_data) return;
 
@@ -187,6 +187,9 @@ info_box(struct terminal *term, enum msgbox_flags flags,
 	 unsigned char *text)
 {
 	/* [gettext_accelerator_context(info_box)] */
-	return msg_box(term, NULL, flags, title, align, text,
-		       NULL, 1, N_("~OK"), NULL, B_ENTER | B_ESC);
+	return msg_box(term, NULL, flags,
+		       title, align,
+		       text,
+		       NULL, 1,
+		       MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC));
 }
diff --git a/src/bfu/msgbox.h b/src/bfu/msgbox.h
index 3ed0848b0..2e06fe8ae 100644
--- a/src/bfu/msgbox.h
+++ b/src/bfu/msgbox.h
@@ -64,7 +64,7 @@ enum msgbox_flags {
  * @udata	Is a reference to any data that should be passed to
  *		the handlers associated with each button. NULL if none.
  *
- * @buttons	Denotes the number of buttons given as varadic arguments.
+ * @buttons	Denotes the number of buttons given as variadic arguments.
  *		For each button 3 arguments are extracted:
  *			o First the label text. It is automatically localized
  *			  unless MSGBOX_NO_INTL is passed. If NULL, this button
@@ -72,6 +72,10 @@ enum msgbox_flags {
  *			o Second pointer to the handler function (taking
  *			  one (void *), which is incidentally the udata).
  *			o Third any flags.
+ *		Each triple should be wrapped in the MSG_BOX_BUTTON
+ *		macro, which converts the values to the correct types.
+ *		(The compiler can't do that on its own for variadic
+ *		arguments.)
  *
  * Note that you should ALWAYS format the msg_box() call like:
  *
@@ -79,9 +83,9 @@ enum msgbox_flags {
  *         title, align,
  *         text,
  *         udata, M,
- *         label1, handler1, flags1,
+ *         MSG_BOX_BUTTON(label1, handler1, flags1),
  *         ...,
- *         labelM, handlerM, flagsM);
+ *         MSG_BOX_BUTTON(labelM, handlerM, flagsM));
  *
  * ...no matter that it could fit on one line in case of a tiny message box. */
 struct dialog_data *
@@ -89,6 +93,21 @@ msg_box(struct terminal *term, struct memory_list *mem_list,
 	enum msgbox_flags flags, unsigned char *title, enum format_align align,
 	unsigned char *text, void *udata, int buttons, ...);
 
+/* Cast @value to @type and warn if the conversion is suspicious.
+ * If @value has side effects, this does them only once.
+ * The expression used here is intended to be standard C, but it is
+ * somewhat tricky.  If it causes trouble on some compiler, you can
+ * #ifdef an alternative definition that skips the type check.  */
+#define MSG_BOX_CAST(type, value) \
+	(((void) sizeof(((int (*)(type)) 0)(value))), (type) (value))
+
+/* A button in the variadic arguments of msg_box().
+ * This macro expands into three arguments.  */
+#define MSG_BOX_BUTTON(label, handler, flags) \
+	MSG_BOX_CAST(const unsigned char *, label), \
+	MSG_BOX_CAST(done_handler_T *, handler), \
+	MSG_BOX_CAST(int, flags)
+
 
 /* msg_text() is basically an equivalent to asprintf(), specifically to be used
  * inside of message boxes. Please always use msg_text() instead of asprintf()
diff --git a/src/config/dialogs.c b/src/config/dialogs.c
index 35d893c48..b90add053 100644
--- a/src/config/dialogs.c
+++ b/src/config/dialogs.c
@@ -54,8 +54,8 @@ write_config_dialog(struct terminal *term, unsigned char *config_file,
 			msg_text(term, N_("Options were saved successfully to config file %s."),
 				 config_file),
 			NULL, 2,
-			N_("~OK"), NULL, B_ENTER | B_ESC,
-			N_("~Do not show anymore"), disable_success_msgbox, 0);
+			MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC),
+			MSG_BOX_BUTTON(N_("~Do not show anymore"), disable_success_msgbox, 0));
 		return;
 	}
 
@@ -815,8 +815,8 @@ really_add_keybinding(void *data, unsigned char *keystroke)
 				 canonical.length ? canonical.source : keystroke,
 				 get_action_name(hop->keymap_id, action_id)),
 			new_hop, 2,
-			N_("~Yes"), really_really_add_keybinding, B_ENTER,
-			N_("~No"), NULL, B_ESC);
+			MSG_BOX_BUTTON(N_("~Yes"), really_really_add_keybinding, B_ENTER),
+			MSG_BOX_BUTTON(N_("~No"), NULL, B_ESC));
 
 		done_string(&canonical); /* safe even if init failed */
 		return;
diff --git a/src/cookies/dialogs.c b/src/cookies/dialogs.c
index 1b8101668..27bcab9f4 100644
--- a/src/cookies/dialogs.c
+++ b/src/cookies/dialogs.c
@@ -50,6 +50,18 @@ add_cookie_info_to_string(struct string *string, struct cookie *cookie,
 			     _(cookie->secure ? N_("yes") : N_("no"), term));
 }
 
+static void
+accept_cookie_in_msg_box(void *cookie_)
+{
+	accept_cookie((struct cookie *) cookie_);
+}
+
+static void
+reject_cookie_in_msg_box(void *cookie_)
+{
+	done_cookie((struct cookie *) cookie_);
+}
+
 /* TODO: Store cookie in data arg. --jonas*/
 void
 accept_cookie_dialog(struct session *ses, void *data)
@@ -78,8 +90,8 @@ accept_cookie_dialog(struct session *ses, void *data)
 		N_("Accept cookie?"), ALIGN_LEFT,
 		string.source,
 		cookie, 2,
-		N_("~Accept"), accept_cookie, B_ENTER,
-		N_("~Reject"), done_cookie, B_ESC);
+		MSG_BOX_BUTTON(N_("~Accept"), accept_cookie_in_msg_box, B_ENTER),
+		MSG_BOX_BUTTON(N_("~Reject"), reject_cookie_in_msg_box, B_ESC));
 }
 
 
diff --git a/src/dialogs/info.c b/src/dialogs/info.c
index f9b6e8b4d..0117418fa 100644
--- a/src/dialogs/info.c
+++ b/src/dialogs/info.c
@@ -131,8 +131,8 @@ menu_keys(struct terminal *term, void *d_, void *xxx)
 		N_("Keys"), ALIGN_LEFT,
 		keys.source,
 		info, 2,
-		N_("~OK"), NULL, B_ENTER | B_ESC,
-		N_("~Toggle display"), push_toggle_keys_display_button, B_ENTER);
+		MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC),
+		MSG_BOX_BUTTON(N_("~Toggle display"), push_toggle_keys_display_button, B_ENTER));
 }
 
 void
diff --git a/src/dialogs/menu.c b/src/dialogs/menu.c
index 101d97e7d..615e66e3e 100644
--- a/src/dialogs/menu.c
+++ b/src/dialogs/menu.c
@@ -100,15 +100,19 @@ save_url_as(struct session *ses)
 		     NULL);
 }
 
-void
-really_exit_prog(struct session *ses)
+static void
+really_exit_prog(void *ses_)
 {
+	struct session *ses = ses_;
+
 	register_bottom_half(destroy_terminal, ses->tab->term);
 }
 
 static inline void
-dont_exit_prog(struct session *ses)
+dont_exit_prog(void *ses_)
 {
+	struct session *ses = ses_;
+
 	ses->exit_query = 0;
 }
 
@@ -124,8 +128,8 @@ query_exit(struct session *ses)
 		     "(and terminate all downloads)?")
 		: N_("Do you really want to exit ELinks?"),
 		ses, 2,
-		N_("~Yes"), (void (*)(void *)) really_exit_prog, B_ENTER,
-		N_("~No"), (void (*)(void *)) dont_exit_prog, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), really_exit_prog, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), dont_exit_prog, B_ESC));
 }
 
 void
diff --git a/src/dialogs/menu.h b/src/dialogs/menu.h
index 4d0077bd1..c5848c600 100644
--- a/src/dialogs/menu.h
+++ b/src/dialogs/menu.h
@@ -24,7 +24,6 @@ void free_history_lists(void);
 
 void query_file(struct session *, struct uri *, void *, void (*)(void *, unsigned char *), void (*)(void *), int);
 
-void really_exit_prog(struct session *ses);
 void query_exit(struct session *ses);
 void exit_prog(struct session *ses, int query);
 
diff --git a/src/formhist/formhist.c b/src/formhist/formhist.c
index c1227f0ab..cea478a91 100644
--- a/src/formhist/formhist.c
+++ b/src/formhist/formhist.c
@@ -330,20 +330,31 @@ forget_forms_with_url(unsigned char *url)
 	return count;
 }
 
-/* Appends form data @form1 (url and submitted_value(s)) to the password file.
- * Returns 1 on success, 0 otherwise. */
-static int
-remember_form(struct formhist_data *form)
+/* Appends form data @form_ (url and submitted_value(s)) to the password file. */
+static void
+remember_form(void *form_)
 {
+	struct formhist_data *form = form_;
+
 	forget_forms_with_url(form->url);
 	add_to_list(saved_forms, form);
 
-	return save_formhist_to_file();
+	save_formhist_to_file();
 }
 
-static int
-never_for_this_site(struct formhist_data *form)
+static void
+dont_remember_form(void *form_)
 {
+	struct formhist_data *form = form_;
+
+	done_formhist_item(form);
+}
+
+static void
+never_for_this_site(void *form_)
+{
+	struct formhist_data *form = form_;
+
 	form->dontsave = 1;
 	return remember_form(form);
 }
@@ -416,9 +427,9 @@ memorize_form(struct session *ses, struct list_head *submit,
 		"obscured (but unencrypted) in a file on your disk.\n\n"
 		"If you are using a valuable password, answer NO."),
 		form, 3,
-		N_("~Yes"), remember_form, B_ENTER,
-		N_("~No"), done_formhist_item, B_ESC,
-		N_("Ne~ver for this site"), never_for_this_site, NULL);
+		MSG_BOX_BUTTON(N_("~Yes"), remember_form, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), dont_remember_form, B_ESC),
+		MSG_BOX_BUTTON(N_("Ne~ver for this site"), never_for_this_site, 0));
 
 	return;
 
diff --git a/src/mime/dialogs.c b/src/mime/dialogs.c
index fc90cc26e..2a67fcfde 100644
--- a/src/mime/dialogs.c
+++ b/src/mime/dialogs.c
@@ -67,8 +67,8 @@ menu_del_ext(struct terminal *term, void *fcp, void *xxx2)
 		msg_text(term, N_("Delete extension %s -> %s?"),
 			 extension, opt->value.string),
 		extension, 2,
-		N_("~Yes"), really_del_ext, B_ENTER,
-		N_("~No"), NULL, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), really_del_ext, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), NULL, B_ESC));
 }
 
 
diff --git a/src/protocol/protocol.c b/src/protocol/protocol.c
index 3ffca54c5..d7d2e71af 100644
--- a/src/protocol/protocol.c
+++ b/src/protocol/protocol.c
@@ -233,7 +233,7 @@ generic_external_protocol_handler(struct session *ses, struct uri *uri)
 				   "%s protocol support"),
 				protocol_backends[uri->protocol].name),
 			ses, 1,
-			N_("~OK"), NULL, B_ENTER | B_ESC);
+			MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC));
 		return;
 	}
 
diff --git a/src/scripting/python/dialogs.c b/src/scripting/python/dialogs.c
index 009ede76c..da096cb7c 100644
--- a/src/scripting/python/dialogs.c
+++ b/src/scripting/python/dialogs.c
@@ -83,7 +83,7 @@ python_info_box(PyObject *self, PyObject *args, PyObject *kwargs)
 		       title, ALIGN_LEFT,
 		       text,
 		       NULL, 1,
-		       N_("~OK"), NULL, B_ENTER | B_ESC);
+		       MSG_BOX_BUTTON(N_("~OK"), NULL, B_ENTER | B_ESC));
 
 	Py_INCREF(Py_None);
 	return Py_None;
diff --git a/src/session/download.c b/src/session/download.c
index ee9917024..fdb41a191 100644
--- a/src/session/download.c
+++ b/src/session/download.c
@@ -493,16 +493,20 @@ struct cdf_hop {
 };
 
 static void
-lun_alternate(struct lun_hop *lun_hop)
+lun_alternate(void *lun_hop_)
 {
+	struct lun_hop *lun_hop = lun_hop_;
+
 	lun_hop->callback(lun_hop->term, lun_hop->file, lun_hop->data, 0);
 	mem_free_if(lun_hop->ofile);
 	mem_free(lun_hop);
 }
 
 static void
-lun_cancel(struct lun_hop *lun_hop)
+lun_cancel(void *lun_hop_)
 {
+	struct lun_hop *lun_hop = lun_hop_;
+
 	lun_hop->callback(lun_hop->term, NULL, lun_hop->data, 0);
 	mem_free_if(lun_hop->ofile);
 	mem_free_if(lun_hop->file);
@@ -510,8 +514,10 @@ lun_cancel(struct lun_hop *lun_hop)
 }
 
 static void
-lun_overwrite(struct lun_hop *lun_hop)
+lun_overwrite(void *lun_hop_)
 {
+	struct lun_hop *lun_hop = lun_hop_;
+
 	lun_hop->callback(lun_hop->term, lun_hop->ofile, lun_hop->data, 0);
 	mem_free_if(lun_hop->file);
 	mem_free(lun_hop);
@@ -520,8 +526,9 @@ lun_overwrite(struct lun_hop *lun_hop)
 static void common_download_do(struct terminal *term, int fd, void *data, int resume);
 
 static void
-lun_resume(struct lun_hop *lun_hop)
+lun_resume(void *lun_hop_)
 {
+	struct lun_hop *lun_hop = lun_hop_;
 	struct cdf_hop *cdf_hop = lun_hop->data;
 
 	int magic = *(int *)cdf_hop->data;
@@ -631,10 +638,10 @@ lookup_unique_name(struct terminal *term, unsigned char *ofile, int resume,
 			empty_string_or_(lun_hop->ofile),
 			empty_string_or_(file)),
 		lun_hop, 4,
-		N_("Sa~ve under the alternative name"), lun_alternate, B_ENTER,
-		N_("~Overwrite the original file"), lun_overwrite, 0,
-		N_("~Resume download of the original file"), lun_resume, 0,
-		N_("~Cancel"), lun_cancel, B_ESC);
+		MSG_BOX_BUTTON(N_("Sa~ve under the alternative name"), lun_alternate, B_ENTER),
+		MSG_BOX_BUTTON(N_("~Overwrite the original file"), lun_overwrite, 0),
+		MSG_BOX_BUTTON(N_("~Resume download of the original file"), lun_resume, 0),
+		MSG_BOX_BUTTON(N_("~Cancel"), lun_cancel, B_ESC));
 }
 
 
diff --git a/src/session/session.c b/src/session/session.c
index 79e4ea8ee..04d3f7c61 100644
--- a/src/session/session.c
+++ b/src/session/session.c
@@ -804,7 +804,7 @@ setup_first_session(struct session *ses, struct uri *uri)
 			"Press ESC for menu. Documentation is available in "
 			"Help menu."),
 			ses, 1,
-			N_("~OK"), handler, B_ENTER | B_ESC);
+			MSG_BOX_BUTTON(N_("~OK"), handler, B_ENTER | B_ESC));
 
 		/* If there is no URI the goto dialog will pop up so there is
 		 * no need to call setup_session(). */
diff --git a/src/session/task.c b/src/session/task.c
index 0595a8468..27e2f55cb 100644
--- a/src/session/task.c
+++ b/src/session/task.c
@@ -85,8 +85,10 @@ ses_load(struct session *ses, struct uri *uri, unsigned char *target_frame,
 }
 
 static void
-post_yes(struct task *task)
+post_yes(void *task_)
 {
+	struct task *task = task_;
+
 	abort_preloading(task->ses, 0);
 
 	/* XXX: Make the session inherit the URI. */
@@ -96,8 +98,10 @@ post_yes(struct task *task)
 }
 
 static void
-post_no(struct task *task)
+post_no(void *task_)
 {
+	struct task *task = task_;
+
 	reload(task->ses, CACHE_MODE_NORMAL);
 	done_uri(task->uri);
 }
@@ -270,8 +274,8 @@ ses_goto(struct session *ses, struct uri *uri, unsigned char *target_frame,
 		N_("Warning"), ALIGN_CENTER,
 		message,
 		task, 2,
-		N_("~Yes"), post_yes, B_ENTER,
-		N_("~No"), post_no, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), post_yes, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), post_no, B_ESC));
 }
 
 
diff --git a/src/terminal/tab.c b/src/terminal/tab.c
index 24ac7579f..8aaf8a38d 100644
--- a/src/terminal/tab.c
+++ b/src/terminal/tab.c
@@ -169,8 +169,9 @@ switch_current_tab(struct session *ses, int direction)
 }
 
 static void
-really_close_tab(struct session *ses)
+really_close_tab(void *ses_)
 {
+	struct session *ses = ses_;
 	struct terminal *term = ses->tab->term;
 	struct window *current_tab = get_current_tab(term);
 
@@ -203,13 +204,14 @@ close_tab(struct terminal *term, struct session *ses)
 		N_("Close tab"), ALIGN_CENTER,
 		N_("Do you really want to close the current tab?"),
 		ses, 2,
-		N_("~Yes"), (void (*)(void *)) really_close_tab, B_ENTER,
-		N_("~No"), NULL, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), really_close_tab, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), NULL, B_ESC));
 }
 
 static void
-really_close_tabs(struct session *ses)
+really_close_tabs(void *ses_)
 {
+	struct session *ses = ses_;
 	struct terminal *term = ses->tab->term;
 	struct window *current_tab = get_current_tab(term);
 	struct window *tab;
@@ -246,8 +248,8 @@ close_all_tabs_but_current(struct session *ses)
 		N_("Close tab"), ALIGN_CENTER,
 		N_("Do you really want to close all except the current tab?"),
 		ses, 2,
-		N_("~Yes"), (void (*)(void *)) really_close_tabs, B_ENTER,
-		N_("~No"), NULL, B_ESC);
+		MSG_BOX_BUTTON(N_("~Yes"), really_close_tabs, B_ENTER),
+		MSG_BOX_BUTTON(N_("~No"), NULL, B_ESC));
 }