diff --git a/src/evdev-tablet-pad.c b/src/evdev-tablet-pad.c
index cb02726a..431972ae 100644
--- a/src/evdev-tablet-pad.c
+++ b/src/evdev-tablet-pad.c
@@ -369,7 +369,7 @@ pad_notify_button_mask(struct pad_dispatch *pad,
 		code = i * 8;
 		while (buttons_slice) {
 			int enabled;
-			char map;
+			key_or_button_map_t map;
 
 			code++;
 			enabled = (buttons_slice & 1);
@@ -379,10 +379,21 @@ pad_notify_button_mask(struct pad_dispatch *pad,
 				continue;
 
 			map = pad->button_map[code - 1];
-			if (map != -1) {
-				group = pad_button_get_mode_group(pad, map);
-				pad_button_update_mode(group, map, state);
-				tablet_pad_notify_button(base, time, map, state, group);
+			if (map_is_unmapped(map))
+				continue;
+
+			if (map_is_button(map)) {
+				int32_t button = map_value(map);
+
+				group = pad_button_get_mode_group(pad, button);
+				pad_button_update_mode(group, button, state);
+				tablet_pad_notify_button(base,
+							 time,
+							 button,
+							 state,
+							 group);
+			} else {
+				abort();
 			}
 		}
 	}
@@ -554,7 +565,7 @@ pad_init_buttons_from_libwacom(struct pad_dispatch *pad,
 		if (code == 0)
 			continue;
 
-		pad->button_map[code] = map++;
+		map_set_button_map(pad->button_map[code], map++);
 	}
 
 	pad->nbuttons = map;
@@ -579,22 +590,22 @@ pad_init_buttons_from_kernel(struct pad_dispatch *pad,
 	/* we match wacom_report_numbered_buttons() from the kernel */
 	for (code = BTN_0; code < BTN_0 + 10; code++) {
 		if (libevdev_has_event_code(device->evdev, EV_KEY, code))
-			pad->button_map[code] = map++;
+			map_set_button_map(pad->button_map[code], map++);
 	}
 
 	for (code = BTN_BASE; code < BTN_BASE + 2; code++) {
 		if (libevdev_has_event_code(device->evdev, EV_KEY, code))
-			pad->button_map[code] = map++;
+			map_set_button_map(pad->button_map[code], map++);
 	}
 
 	for (code = BTN_A; code < BTN_A + 6; code++) {
 		if (libevdev_has_event_code(device->evdev, EV_KEY, code))
-			pad->button_map[code] = map++;
+			map_set_button_map(pad->button_map[code], map++);
 	}
 
 	for (code = BTN_LEFT; code < BTN_LEFT + 7; code++) {
 		if (libevdev_has_event_code(device->evdev, EV_KEY, code))
-			pad->button_map[code] = map++;
+			map_set_button_map(pad->button_map[code], map++);
 	}
 
 	pad->nbuttons = map;
@@ -607,7 +618,7 @@ pad_init_buttons(struct pad_dispatch *pad,
 	size_t i;
 
 	for (i = 0; i < ARRAY_LENGTH(pad->button_map); i++)
-		pad->button_map[i] = -1;
+		map_init(pad->button_map[i]);
 
 	if (!pad_init_buttons_from_libwacom(pad, device))
 		pad_init_buttons_from_kernel(pad, device);
diff --git a/src/evdev-tablet-pad.h b/src/evdev-tablet-pad.h
index 6208caf8..feb95272 100644
--- a/src/evdev-tablet-pad.h
+++ b/src/evdev-tablet-pad.h
@@ -47,6 +47,18 @@ struct button_state {
 	unsigned char bits[NCHARS(KEY_CNT)];
 };
 
+typedef struct {
+	uint32_t value;
+} key_or_button_map_t;
+
+#define map_init(x_) ((x_).value = (uint32_t)-1)
+#define map_is_unmapped(x_) ((x_).value == (uint32_t)-1)
+#define map_is_button(x_) (((x_).value & 0xFF000000) == 0)
+#define map_is_key(x_) (((x_).value & 0xFF000000) != 0)
+#define map_set_button_map(field_, value_) ((field_).value = value_)
+#define map_set_key_map(field_, value_) ((field_).value = value_ | 0xFF000000)
+#define map_value(x_) ((x_).value & 0x00FFFFFF)
+
 struct pad_dispatch {
 	struct evdev_dispatch base;
 	struct evdev_device *device;
@@ -56,7 +68,7 @@ struct pad_dispatch {
 	struct button_state button_state;
 	struct button_state prev_button_state;
 
-	char button_map[KEY_CNT];
+	key_or_button_map_t button_map[KEY_CNT];
 	unsigned int nbuttons;
 
 	bool have_abs_misc_terminator;