diff --git a/src/texteff.cpp b/src/texteff.cpp
--- a/src/texteff.cpp
+++ b/src/texteff.cpp
@@ -55,7 +55,7 @@ static bool _textmessage_visible = false
 /* The chatbox grows from the bottom so the coordinates are pixels from
  * the left and pixels from the bottom. The height is the maximum height */
 static const Oblong _textmsg_box = {10, 30, 500, 150};
-static uint8 _textmessage_backup[150 * 500 * 4]; // (height * width)
+static uint8 _textmessage_backup[150 * 500 * 5]; // (height * width)
 
 static inline uint GetTextMessageCount()
 {
@@ -163,7 +163,7 @@ void UndrawTextMessage()
 
 		_textmessage_visible = false;
 		/* Put our 'shot' back to the screen */
-		blitter->CopyFromBuffer(blitter->MoveTo(_screen.dst_ptr, x, y), _textmessage_backup, width, height, _textmsg_box.width);
+		blitter->CopyFromBuffer(blitter->MoveTo(_screen.dst_ptr, x, y), _textmessage_backup, width, height);
 		/* And make sure it is updated next time */
 		_video_driver->make_dirty(x, y, width, height);
 
@@ -223,8 +223,10 @@ void DrawTextMessage()
 	}
 	if (width <= 0 || height <= 0) return;
 
+	assert(blitter->BufferSize(width, height) < (int)sizeof(_textmessage_backup));
+
 	/* Make a copy of the screen as it is before painting (for undraw) */
-	blitter->CopyToBuffer(blitter->MoveTo(_screen.dst_ptr, x, y), _textmessage_backup, width, height, _textmsg_box.width);
+	blitter->CopyToBuffer(blitter->MoveTo(_screen.dst_ptr, x, y), _textmessage_backup, width, height);
 
 	_cur_dpi = &_screen; // switch to _screen painting