diff --git a/Makefile b/Makefile
index 93cd52d..86115c7 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ DEBUGOBJDIR = tmp/$(OSDIRNAME)/debug
 LIBDIR = lib/$(OSDIRNAME)
 BINDIR = bin/$(OSDIRNAME)
 
-CXXFLAGS = -std=c++11 -I include -isystem /usr/include -I$(SRCDIR) -I$(RESDIR)
+CXXFLAGS = -std=c++11 -I include -I /usr/include -I$(SRCDIR) -I$(RESDIR)
 LDFLAGS = $(wildcard $(LIBDIR)/*.a) -lm -lpng -lz -lXfixes -lXext -lXft -lfontconfig -lXinerama -lpthread -ldl -lX11 -lXpm -lXrender
 
 RELEASEFLAGS = -DNDEBUG -O3 -flto -march=native
diff --git a/TODO.md b/TODO.md
index 11b8c64..a490287 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,7 +1,6 @@
 # To Do
 
 * **Add:** Undo + Redo
-* **Add:** Add + remove metatiles
 * **Fix:** incorrect sidebar size when resizing window (sometimes)
 
 
@@ -10,7 +9,7 @@
 * More color schemes than just Day, Nite, and Indoor
 * Change color schemes for an already-open map
 * Swap tilesets for an already-open map
-* Use IFileOpenDialog, not SHBrowseForFolder, for new maps
+* Use IFileOpenDialog, not SHBrowseForFolder, for new maps (Windows only)
 
 
 ## Never
diff --git a/src/main-window.cpp b/src/main-window.cpp
index 42fd93b..ef75bff 100644
--- a/src/main-window.cpp
+++ b/src/main-window.cpp
@@ -584,8 +584,43 @@ void Main_Window::open_map(const char *directory, const char *filename) {
 	redraw();
 }
 
-void Main_Window::add_sub_metatiles(int n) {
-	// TODO: add/remove blocks
+void Main_Window::add_sub_metatiles(size_t n) {
+	size_t s = _metatileset.size();
+	if (n == s) { return; }
+	_metatileset.size(n);
+	int ms = metatile_size();
+
+	if (n > s) {
+		// add metatiles
+		for (int i = (int)s; i < n; i++) {
+			int x = ms * (i % METATILES_PER_ROW), y = ms * (i / METATILES_PER_ROW);
+			Metatile_Button *mtb = new Metatile_Button(_sidebar->x() + x, _sidebar->y() + y, ms, (uint8_t)i);
+			mtb->callback((Fl_Callback *)select_metatile_cb, this);
+			_sidebar->add(mtb);
+			_metatile_buttons[i] = mtb;
+		}
+	}
+	else if (n < s) {
+		// remove metatiles
+		if (_selected->id() >= n) {
+			_selected = _metatile_buttons[0];
+			_selected->setonly();
+			_sidebar->scroll_to(0, 0);
+		}
+		for (int i = (int)n; i < s; i++) {
+			_sidebar->remove((int)n);
+			_metatile_buttons[i] = NULL;
+		}
+	}
+
+	_sidebar->size(ms * METATILES_PER_ROW + Fl::scrollbar_size(), _sidebar->h());
+	_sidebar->init_sizes();
+	_sidebar->contents(ms * METATILES_PER_ROW, ms * (((int)_metatileset.size() + METATILES_PER_ROW - 1) / METATILES_PER_ROW));
+
+	update_labels();
+	update_status(NULL);
+
+	redraw();
 }
 
 void Main_Window::resize_map(int w, int h) {
@@ -1008,8 +1043,9 @@ void Main_Window::redo_cb(Fl_Widget *, Main_Window *) {
 
 void Main_Window::add_sub_cb(Fl_Widget *, Main_Window *mw) {
 	if (!mw->_map.size()) { return; }
-	mw->_add_sub_dialog->num_metatiles((uint8_t)mw->_metatileset.size());
+	mw->_add_sub_dialog->num_metatiles(mw->_metatileset.size());
 	mw->_add_sub_dialog->show(mw);
+	if (mw->_add_sub_dialog->canceled()) { return; }
 	if (mw->_add_sub_dialog->num_metatiles() != mw->_metatileset.size()) {
 		mw->add_sub_metatiles((int)mw->_add_sub_dialog->num_metatiles());
 	}
@@ -1019,6 +1055,7 @@ void Main_Window::resize_cb(Fl_Widget *, Main_Window *mw) {
 	if (!mw->_map.size()) { return; }
 	mw->_resize_dialog->map_size(mw->_map.width(), mw->_map.height());
 	mw->_resize_dialog->show(mw);
+	if (mw->_resize_dialog->canceled()) { return; }
 	if (mw->_resize_dialog->map_width() != mw->_map.width() || mw->_resize_dialog->map_height() != mw->_map.height()) {
 		mw->resize_map(mw->_resize_dialog->map_width(), mw->_resize_dialog->map_height());
 	}
diff --git a/src/main-window.h b/src/main-window.h
index dc5bbdc..c1a0c37 100644
--- a/src/main-window.h
+++ b/src/main-window.h
@@ -77,7 +77,7 @@ class Main_Window : public Fl_Double_Window {
 	void open_map(const char *filename);
 private:
 	void open_map(const char *directory, const char *filename);
-	void add_sub_metatiles(int n);
+	void add_sub_metatiles(size_t n);
 	void resize_map(int w, int h);
 	bool save_map(void);
 	bool save_metatileset(void);
diff --git a/src/metatileset.cpp b/src/metatileset.cpp
index a9109f9..4ceaaf4 100644
--- a/src/metatileset.cpp
+++ b/src/metatileset.cpp
@@ -29,19 +29,35 @@ void Metatileset::clear() {
 	_modified = false;
 }
 
+void Metatileset::size(size_t n) {
+	size_t low = MIN(n, _num_metatiles), high = MAX(n, _num_metatiles);
+	for (size_t i = low; i < high; i++) {
+		_metatiles[i]->clear();
+	}
+	_num_metatiles = n;
+	_modified = true;
+}
+
 void Metatileset::draw_metatile(int x, int y, uint8_t id, bool z) const {
-	Metatile *mt = _metatiles[id];
-	int s = TILE_SIZE * (z ? ZOOM_FACTOR : 1);
-	int d = NUM_CHANNELS * (z ? 1 : ZOOM_FACTOR);
-	int ld = LINE_BYTES * (z ? 1 : ZOOM_FACTOR);
-	for (int ty = 0; ty < METATILE_SIZE; ty++) {
-		for (int tx = 0; tx < METATILE_SIZE; tx++) {
-			uint8_t tid = mt->tile_id(tx, ty);
-			const Tile *t = _tileset.tile(tid);
-			const uchar *rgb = t->rgb();
-			fl_draw_image(rgb, x + tx * s, y + ty * s, s, s, d, ld);
+	if (id < size()) {
+		Metatile *mt = _metatiles[id];
+		int s = TILE_SIZE * (z ? ZOOM_FACTOR : 1);
+		int d = NUM_CHANNELS * (z ? 1 : ZOOM_FACTOR);
+		int ld = LINE_BYTES * (z ? 1 : ZOOM_FACTOR);
+		for (int ty = 0; ty < METATILE_SIZE; ty++) {
+			for (int tx = 0; tx < METATILE_SIZE; tx++) {
+				uint8_t tid = mt->tile_id(tx, ty);
+				const Tile *t = _tileset.tile(tid);
+				const uchar *rgb = t->rgb();
+				fl_draw_image(rgb, x + tx * s, y + ty * s, s, s, d, ld);
+			}
 		}
 	}
+	else {
+		int s = TILE_SIZE * METATILE_SIZE * (z ? ZOOM_FACTOR : 1);
+		fl_color(EMPTY_RGB);
+		fl_rectf(x, y, s, s);
+	}
 }
 
 uchar *Metatileset::print_rgb(const Map &map) const {
diff --git a/src/metatileset.h b/src/metatileset.h
index 57019ce..5c05e79 100644
--- a/src/metatileset.h
+++ b/src/metatileset.h
@@ -21,6 +21,7 @@ class Metatileset {
 	Metatileset();
 	~Metatileset();
 	inline size_t size(void) const { return _num_metatiles; }
+	void size(size_t n);
 	inline Tileset *tileset(void) { return &_tileset; }
 	inline Metatile *metatile(uint8_t id) { return _metatiles[id]; }
 	inline Result result(void) const { return _result; }
diff --git a/src/tileset.cpp b/src/tileset.cpp
index da2a9e9..308116e 100644
--- a/src/tileset.cpp
+++ b/src/tileset.cpp
@@ -1,8 +1,10 @@
 #include "tiled-image.h"
 #include "tileset.h"
 
+const uchar empty_rgb[NUM_CHANNELS] = {EMPTY_RGB};
+
 // Tileset.Lighting x Palette_Map.Palette x Tile.Hue x RGB
-static const uchar tileset_colors[3][9][4][3] = {
+static const uchar tileset_colors[3][9][4][NUM_CHANNELS] = {
 	{ // DAY
 		// WHITE, DARK, LIGHT, BLACK
 		{{8*27, 8*31, 8*27}, {8*13, 8*13, 8*13}, {8*21, 8*21, 8*21}, {8* 7, 8* 7, 8* 7}}, // GRAY
@@ -13,7 +15,7 @@ static const uchar tileset_colors[3][9][4][3] = {
 		{{8*27, 8*31, 8*27}, {8*20, 8*15, 8* 3}, {8*24, 8*18, 8* 7}, {8* 7, 8* 7, 8* 7}}, // BROWN
 		{{8*27, 8*31, 8*27}, {8* 5, 8*17, 8*31}, {8*15, 8*31, 8*31}, {8* 7, 8* 7, 8* 7}}, // ROOF
 		{{8*31, 8*31, 8*16}, {8*14, 8* 9, 8* 0}, {8*31, 8*31, 8*16}, {8* 0, 8* 0, 8* 0}}, // TEXT
-		{{0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}}, // UNDEFINED
+		{{EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB}       }, // UNDEFINED
 	},
 	{ // NITE
 		// WHITE, DARK, LIGHT, BLACK
@@ -25,7 +27,7 @@ static const uchar tileset_colors[3][9][4][3] = {
 		{{8*15, 8*14, 8*24}, {8* 8, 8* 4, 8* 5}, {8*12, 8* 9, 8*15}, {8* 0, 8* 0, 8* 0}}, // BROWN
 		{{8*15, 8*14, 8*24}, {8*11, 8* 9, 8*20}, {8*13, 8*12, 8*23}, {8* 0, 8* 0, 8* 0}}, // ROOF
 		{{8*31, 8*31, 8*16}, {8*14, 8* 9, 8* 0}, {8*31, 8*31, 8*16}, {8* 0, 8* 0, 8* 0}}, // TEXT
-		{{0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}}, // UNDEFINED
+		{{EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB}       }, // UNDEFINED
 	},
 	{ // INDOOR
 		// WHITE, DARK, LIGHT, BLACK
@@ -37,7 +39,7 @@ static const uchar tileset_colors[3][9][4][3] = {
 		{{8*26, 8*24, 8*17}, {8*16, 8*13, 8* 3}, {8*21, 8*17, 8* 7}, {8* 7, 8* 7, 8* 7}}, // BROWN
 		{{8*30, 8*28, 8*26}, {8*14, 8*16, 8*31}, {8*17, 8*19, 8*31}, {8* 7, 8* 7, 8* 7}}, // ROOF
 		{{8*31, 8*31, 8*16}, {8*14, 8* 9, 8* 0}, {8*31, 8*31, 8*16}, {8* 0, 8* 0, 8* 0}}, // TEXT
-		{{0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}, {0xAB, 0xCD, 0xEF}}, // UNDEFINED
+		{{EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB},        {EMPTY_RGB}       }, // UNDEFINED
 	},
 };
 
diff --git a/src/tileset.h b/src/tileset.h
index 0966f1e..e655508 100644
--- a/src/tileset.h
+++ b/src/tileset.h
@@ -7,11 +7,14 @@
 #include "palette-map.h"
 #include "utils.h"
 
+#define EMPTY_RGB 0xAB, 0xCD, 0xEF // intentionally leave out parentheses or brackets
+
 class Tileset {
 public:
 	enum Lighting { DAY, NITE, INDOOR };
 	enum Result { GFX_OK, GFX_NO_PALETTE, GFX_BAD_FILE, GFX_BAD_EXT, GFX_BAD_DIMS,
 		GFX_TOO_SHORT, GFX_TOO_LARGE, GFX_NOT_GRAYSCALE, GFX_BAD_CMD, GFX_NULL };
+	static const uchar empty_rgb[NUM_CHANNELS];
 private:
 	std::string _name;
 	Palette_Map _palette_map;
diff --git a/src/version.h b/src/version.h
index 8968d1a..de783b4 100644
--- a/src/version.h
+++ b/src/version.h
@@ -1,11 +1,11 @@
 #ifndef VERSION_H
 #define VERSION_H
 
-#define PROGRAM_VERSION 1,4,1
+#define PROGRAM_VERSION 1,4,2
 #ifdef _DEBUG
-#define PROGRAM_VERSION_STRING "1.4.1 [DEBUG]"
+#define PROGRAM_VERSION_STRING "1.4.2 [DEBUG]"
 #else
-#define PROGRAM_VERSION_STRING "1.4.1"
+#define PROGRAM_VERSION_STRING "1.4.2"
 #endif
 
 #define PROGRAM_NAME "Polished Map"