diff --git a/src/editor.rs b/src/editor.rs
index 24aa9e6..869a708 100644
--- a/src/editor.rs
+++ b/src/editor.rs
@@ -130,7 +130,10 @@ impl Editor {
 
 	fn step(&mut self) {
 		self.machine.step();
-		if self.level.outputs() == self.machine.output() && self.complete_popup == Popup::Start {
+		if !self.level.outputs().is_empty()
+			&& self.level.outputs() == self.machine.output()
+			&& self.complete_popup == Popup::Start
+		{
 			self.complete_popup = Popup::Visible;
 			self.exit_state = ExitState::Save;
 			self.sim_state = SimState::Stepping;
@@ -190,6 +193,9 @@ impl Editor {
 	fn set_tile(&mut self, pos: Pos, tile: Tile) {
 		self.source_board.grow_to_include(pos);
 		self.source_board.set(pos, tile);
+		if tile.is_blank() {
+			self.source_board.trim_size();
+		}
 	}
 
 	pub fn update(&mut self, rl: &RaylibHandle) {
diff --git a/src/marble_engine/board.rs b/src/marble_engine/board.rs
index b3cc8ff..80ad250 100644
--- a/src/marble_engine/board.rs
+++ b/src/marble_engine/board.rs
@@ -204,6 +204,70 @@ impl Board {
 		}
 	}
 
+	pub fn trim_size(&mut self) {
+		{
+			let mut top_blanks = 0;
+			while top_blanks < self.height && self.rows[top_blanks].iter().all(Tile::is_blank) {
+				top_blanks += 1;
+			}
+			let trim_top = top_blanks.saturating_sub(2);
+			for _ in 0..trim_top {
+				self.rows.remove(0);
+			}
+			self.offset_y -= trim_top as isize;
+			self.height -= trim_top;
+		}
+		{
+			let mut bottom_blanks = 0;
+			while bottom_blanks < self.height
+				&& self.rows[self.height - bottom_blanks - 1]
+					.iter()
+					.all(Tile::is_blank)
+			{
+				bottom_blanks += 1;
+			}
+			let trim_bottom = bottom_blanks.saturating_sub(2);
+			for _ in 0..trim_bottom {
+				self.rows.pop();
+			}
+			self.height -= trim_bottom;
+		}
+		{
+			let mut left_blanks = 0;
+			while left_blanks < self.width
+				&& self.rows.iter().all(|row| row[left_blanks].is_blank())
+			{
+				left_blanks += 1;
+			}
+			let trim_left = left_blanks.saturating_sub(2);
+			for row in &mut self.rows {
+				for _ in 0..trim_left {
+					row.remove(0);
+				}
+			}
+			self.offset_x -= trim_left as isize;
+			self.width -= trim_left;
+		}
+		{
+			let mut right_blanks = 0;
+			while right_blanks < self.height
+				&& self
+					.rows
+					.iter()
+					.all(|row| row[self.width - right_blanks - 1].is_blank())
+			{
+				right_blanks += 1;
+			}
+			let trim_right = right_blanks.saturating_sub(2);
+			for row in &mut self.rows {
+				for _ in 0..trim_right {
+					row.pop();
+				}
+			}
+			self.width -= trim_right;
+		}
+	}
+
 	pub fn width(&self) -> usize {
 		self.width
 	}