diff --git a/gtk3/main.c b/gtk3/main.c
index 77d7a6e..8e4619f 100644
--- a/gtk3/main.c
+++ b/gtk3/main.c
@@ -65,9 +65,11 @@ static volatile bool stopping = false;
 
 #define tileset_buffer_length 256 * 192 * 4
 static uint32_t tileset_buffer[tileset_buffer_length] = {0};
+static GMutex tileset_buffer_mutex;
 
 #define tilemap_buffer_length 256 * 256 * 4
 static uint32_t tilemap_buffer[tilemap_buffer_length] = {0};
+static GMutex tilemap_buffer_mutex;
 
 static GB_oam_info_t oamInfo[40];
 static uint16_t oamCount;
@@ -240,7 +242,7 @@ static gint handle_local_options(GApplication *app, GVariantDict *options, gpoin
 // and the context it uses is a legacy OpenGL 1.4 context because
 // GTK3 calls OpenGL 2.0+ functions on it.
 gboolean test_gl_support(void) {
-	gboolean result = FALSE;
+	gboolean result = false;
 
 	GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
 	g_signal_connect(window, "realize", G_CALLBACK(gl_check_realize), &result);
@@ -262,7 +264,7 @@ void gl_check_realize(GtkWidget *w, gpointer user_data_gptr) {
 	if (error != NULL) {
 		g_warning("Failed to create context: %s", error->message);
 		g_error_free(error);
-		*result = FALSE;
+		*result = false;
 	}
 	else {
 		gdk_gl_context_make_current(context);
@@ -283,7 +285,7 @@ void gl_check_realize(GtkWidget *w, gpointer user_data_gptr) {
 static gboolean init_controllers() {
 	if (SDL_InitSubSystem(SDL_INIT_GAMECONTROLLER) < 0) {
 		g_warning("Failed to initialize game controller support: %s", SDL_GetError());
-		return FALSE;
+		return false;
 	}
 
 	SDL_QuitSubSystem(SDL_INIT_EVENTS);
@@ -319,7 +321,7 @@ static gboolean init_controllers() {
 		}
 	}
 
-	return TRUE;
+	return true;
 }
 
 static gboolean init_audio() {
@@ -330,7 +332,7 @@ static gboolean init_audio() {
 
 	if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0) {
 		g_warning("Failed to initialize audio: %s", SDL_GetError());
-		return FALSE;
+		return false;
 	}
 
 	memset(&want_aspec, 0, sizeof(want_aspec));
@@ -364,7 +366,7 @@ static gboolean init_audio() {
 	SDL_PauseAudioDevice(device_id, audio_playing? 0 : 1);
 	GB_set_sample_rate(&gb, have_aspec.freq);
 
-	return TRUE;
+	return true;
 }
 
 static GB_model_t get_model() {
@@ -527,11 +529,11 @@ static gboolean scroll_to_bottom(GtkTextView *textview, GtkTextMark *mark) {
 	gtk_text_iter_set_line_offset(&iter, 0);
 
 	gtk_text_buffer_move_mark(buffer, mark, &iter);
-	gtk_text_view_scroll_to_mark(textview, mark, 0.0, TRUE, 0.0, 0.10);
+	gtk_text_view_scroll_to_mark(textview, mark, 0.0, true, 0.0, 0.10);
 
 	gtk_text_buffer_delete_mark(buffer, mark);
 
-	return TRUE;
+	return true;
 }
 
 static void append_pending_output(void) {
@@ -539,7 +541,7 @@ static void append_pending_output(void) {
 
 	if (should_clear_sidebar) {
 		clear_sidebar();
-		should_clear_sidebar = FALSE;
+		should_clear_sidebar = false;
 	}
 
 	if (gtk_text_buffer_get_char_count(pending_console_output) > 0) {
@@ -554,7 +556,7 @@ static void append_pending_output(void) {
 		gtk_text_buffer_get_end_iter(text_buf, &iter);
 		gtk_text_buffer_insert_range(text_buf, &iter, &start, &end);
 
-		scroll_to_bottom(text_view, gtk_text_buffer_create_mark(text_buf, NULL, &iter, TRUE));
+		scroll_to_bottom(text_view, gtk_text_buffer_create_mark(text_buf, NULL, &iter, true));
 
 		gtk_text_buffer_set_text(pending_console_output, "", -1);
 	}
@@ -571,7 +573,7 @@ static void console_log(GB_gameboy_t *gb, const char *string, GB_log_attributes
 
 		// Append attributed text to "pending_console_output" GtkTextBuffer
 		gtk_text_buffer_get_end_iter(pending_console_output, &iter);
-		GtkTextMark *start_mark = gtk_text_buffer_create_mark(pending_console_output, NULL, &iter, TRUE);
+		GtkTextMark *start_mark = gtk_text_buffer_create_mark(pending_console_output, NULL, &iter, true);
 		gtk_text_buffer_insert(pending_console_output, &iter, g_strdup(string), -1);
 		gtk_text_buffer_get_iter_at_mark(pending_console_output, &start, start_mark);
 
@@ -610,7 +612,7 @@ static void create_fallback_canvas(void) {
 	fallback_canvas = GTK_DRAWING_AREA(gtk_drawing_area_new());
 	g_signal_connect(fallback_canvas, "draw", G_CALLBACK(on_draw_fallback), NULL);
 	g_signal_connect(fallback_canvas, "size-allocate", G_CALLBACK(resize), NULL);
-	gtk_box_pack_end(GTK_BOX(main_window_container), GTK_WIDGET(fallback_canvas), TRUE, TRUE, 0);
+	gtk_box_pack_end(GTK_BOX(main_window_container), GTK_WIDGET(fallback_canvas), true, true, 0);
 }
 
 // Create our application’s menu.
@@ -642,11 +644,11 @@ static void setup_menu(GApplication *app) {
 		if (desktop != NULL && show_in_shell) {
 			menubar_type = MENUBAR_SHOW_IN_SHELL;
 		}
-		else if (desktop != NULL && g_str_match_string("GNOME", desktop, FALSE)) {
-			if (g_str_match_string("GNOME-Flashback", desktop, FALSE) || g_str_match_string("GNOME-Classic", desktop, FALSE)) {
+		else if (desktop != NULL && g_str_match_string("GNOME", desktop, false)) {
+			if (g_str_match_string("GNOME-Flashback", desktop, false) || g_str_match_string("GNOME-Classic", desktop, false)) {
 				menubar_type = MENUBAR_SHOW_IN_WINDOW;
 			}
-			else if (gdm_session != NULL && (g_str_match_string("gnome-classic", gdm_session, FALSE) || g_str_match_string("gnome-flashback", gdm_session, FALSE))) {
+			else if (gdm_session != NULL && (g_str_match_string("gnome-classic", gdm_session, false) || g_str_match_string("gnome-flashback", gdm_session, false))) {
 				menubar_type = MENUBAR_SHOW_IN_WINDOW;
 			}
 			else {
@@ -671,7 +673,7 @@ static void setup_menu(GApplication *app) {
 		case MENUBAR_SHOW_IN_WINDOW: {
 			g_debug("Showing menu in the window");
 			GtkMenuBar *menubar = GTK_MENU_BAR(gtk_menu_bar_new_from_model(menubar_model));
-			gtk_box_pack_start(GTK_BOX(main_window_container), GTK_WIDGET(menubar), FALSE, FALSE, 0);
+			gtk_box_pack_start(GTK_BOX(main_window_container), GTK_WIDGET(menubar), false, false, 0);
 			break;
 		}
 
@@ -916,7 +918,7 @@ static void create_canvas() {
 		gtk_gl_area_set_has_depth_buffer(gl_area, false);
 		gtk_gl_area_set_has_stencil_buffer(gl_area, false);
 		g_signal_connect(gl_area, "realize", G_CALLBACK(gl_init), NULL);
-		gtk_box_pack_end(GTK_BOX(main_window_container), GTK_WIDGET(gl_area), TRUE, TRUE, 0);
+		gtk_box_pack_end(GTK_BOX(main_window_container), GTK_WIDGET(gl_area), true, true, 0);
 	}
 	else {
 		create_fallback_canvas();
@@ -938,8 +940,8 @@ static void setup_console() {
 	);
 
 	gtk_text_buffer_create_tag(text_buf, "bold",             "weight",    PANGO_WEIGHT_BOLD, NULL);
-	gtk_text_buffer_create_tag(text_buf, "underline",        "underline", PANGO_UNDERLINE_SINGLE, "underline-set", TRUE, NULL);
-	gtk_text_buffer_create_tag(text_buf, "dashed_underline", "underline", PANGO_UNDERLINE_DOUBLE, "underline-set", TRUE, NULL);
+	gtk_text_buffer_create_tag(text_buf, "underline",        "underline", PANGO_UNDERLINE_SINGLE, "underline-set", true, NULL);
+	gtk_text_buffer_create_tag(text_buf, "dashed_underline", "underline", PANGO_UNDERLINE_DOUBLE, "underline-set", true, NULL);
 
 	g_mutex_init(&debugger_input_mutex);
 	g_cond_init(&debugger_input_cond);
@@ -1085,7 +1087,7 @@ static gboolean on_key_press(GtkWidget *w, GdkEventKey *event, gpointer data) {
 		pressed_buttons &= ~mask;
 	}
 
-	return FALSE;
+	return false;
 }
 
 static void on_window_state_change(GtkWidget *w, GdkEventWindowState *event, gpointer data) {
@@ -1159,14 +1161,25 @@ static void activate_close(GSimpleAction *action, GVariant *parameter, gpointer
 	
 	// Clear the screen as side effect
 	update_window_geometry();
+	gtk_widget_queue_draw(fallback_canvas ? GTK_WIDGET(fallback_canvas) : GTK_WIDGET(gl_area));
 
-	if (fallback_canvas) {
-		gtk_widget_queue_draw(GTK_WIDGET(main_window));
-	}
-	else if (gl_area) {
-		gtk_gl_area_queue_render(gl_area);
-	}
+	// Clear the VRAM viewer
+	g_mutex_lock(&tileset_buffer_mutex);
+	memset(tileset_buffer, 0, sizeof tileset_buffer);
+	g_mutex_unlock(&tileset_buffer_mutex);
+	
+	g_mutex_lock(&tilemap_buffer_mutex);
+	memset(tilemap_buffer, 0, sizeof tilemap_buffer);
+	g_mutex_unlock(&tilemap_buffer_mutex);
 
+	gtk_stack_set_visible_child_name(builder_get(GTK_STACK, "vram_viewer_stack"), "vram_viewer_tileset");
+	gtk_tree_view_set_model(builder_get(GTK_TREE_VIEW, "vram_viewer_sprites"), NULL);
+	gtk_tree_view_set_model(builder_get(GTK_TREE_VIEW, "vram_viewer_palettes"), NULL);
+
+	// Redraw the VRAM viewer
+	gtk_widget_queue_draw(GTK_WIDGET(vram_viewer));
+
+	// Update menu action states
 	action_set_enabled(main_application, "close", false);
 	action_entries_set_enabled(emulation_entries, G_N_ELEMENTS(emulation_entries), false);
 }
@@ -1344,7 +1357,7 @@ static gboolean on_draw_fallback(GtkWidget *widget, cairo_t *cr, gpointer data)
 	cairo_pattern_set_filter(cairo_get_source(cr), CAIRO_FILTER_NEAREST);
 	cairo_paint(cr);
 
-	return FALSE;
+	return false;
 }
 
 // TODO: Comment
@@ -1365,6 +1378,8 @@ static void on_vram_viewer_unrealize() {
 
 // Gets called when the tileset viewer should be redrawn
 static gboolean on_draw_vram_viewer_tileset(GtkWidget *widget, cairo_t *cr, gpointer data) {
+	g_mutex_lock(&tileset_buffer_mutex);
+
 	guint width, height;
 	GtkStyleContext *context;
 
@@ -1411,11 +1426,14 @@ static gboolean on_draw_vram_viewer_tileset(GtkWidget *widget, cairo_t *cr, gpoi
 		cairo_stroke(cr);
 	}
 
-	return FALSE;
+	g_mutex_unlock(&tileset_buffer_mutex);
+	return false;
 }
 
 // Gets called when the tilemap viewer should be redrawn
 static gboolean on_draw_vram_viewer_tilemap(GtkWidget *widget, cairo_t *cr, gpointer data) {
+	g_mutex_lock(&tilemap_buffer_mutex);
+
 	guint width, height;
 	GtkStyleContext *context;
 
@@ -1479,7 +1497,8 @@ static gboolean on_draw_vram_viewer_tilemap(GtkWidget *widget, cairo_t *cr, gpoi
 		cairo_stroke(cr);
 	}
 
-	return FALSE;
+	g_mutex_unlock(&tilemap_buffer_mutex);
+	return false;
 }
 
 static gboolean on_motion_vram_viewer_tileset(GtkWidget *widget, GdkEventMotion *event) {
@@ -1504,7 +1523,7 @@ static gboolean on_motion_vram_viewer_tileset(GtkWidget *widget, GdkEventMotion
 	GtkLabel *status = builder_get(GTK_LABEL, "vram_viewer_status");
 	gtk_label_set_text(status, g_strdup_printf("Tile number $%02x at %d:$%04x", tile & 0xFF, bank, 0x8000 + tile * 0x10));
 
-	return TRUE;
+	return true;
 }
 
 static gboolean on_motion_vram_viewer_tilemap(GtkWidget *widget, GdkEventMotion *event) {
@@ -1581,7 +1600,7 @@ static gboolean on_motion_vram_viewer_tilemap(GtkWidget *widget, GdkEventMotion
 		));
 	}
 
-	return TRUE;
+	return true;
 }
 
 static void on_vram_tab_change(GtkWidget *widget, GParamSpec *pspec, GtkStackSwitcher *self) {