diff --git a/README.md b/README.md
index 0abc5ef..9f84eff 100644
--- a/README.md
+++ b/README.md
@@ -145,7 +145,7 @@ cat samples/ship.ans
 - The Zoom submenu flickers as it opens, and may not always open in the right place.
 - The canvas flickers when zooming in with the Magnifier tool.
 - Some languages don't display correctly.
-- Large files can make the program very slow, as can magnifying the canvas.
+- Large files can make the program very slow, as can magnifying the canvas. There is a 500 KB limit when opening files to prevent it from freezing.
 - Saved ANSI files are unnecessarily large, because they include escape sequences for every cell, even if the colors match the previous cell.
 - Free-Form Select stamping/finalizing is incorrect when the selection is off-screen to the left or top.
 - Moving the selection with the arrow keys does not cut out the selection from the canvas, it only moves the selection box.
diff --git a/src/textual_paint/paint.py b/src/textual_paint/paint.py
index d6451d2..1008862 100755
--- a/src/textual_paint/paint.py
+++ b/src/textual_paint/paint.py
@@ -42,6 +42,8 @@ from wallpaper import get_config_dir, set_wallpaper
 
 from __init__ import __version__
 
+MAX_FILE_SIZE = 500000 # 500 KB
+
 observer = None
 
 def restart_program():
@@ -1898,6 +1900,9 @@ class PaintApp(App[None]):
         print("Checking for backup at:", backup_file_path, "...it exists" if os.path.exists(backup_file_path) else "...it does not exist")
         if os.path.exists(backup_file_path):
             try:
+                if os.path.getsize(backup_file_path) > MAX_FILE_SIZE:
+                    self.message_box(_("Open"), _("A backup file was found, but was not recovered.") + "\n" + _("The file is too large to open."), "ok")
+                    return
                 with open(backup_file_path, "r") as f:
                     backup_content = f.read()
                     backup_image = AnsiArtDocument.from_text(backup_content)
@@ -2218,6 +2223,9 @@ class PaintApp(App[None]):
                 return
 
         try:
+            if os.path.getsize(file_path) > MAX_FILE_SIZE:
+                self.message_box(_("Open"), _("The file is too large to open."), "ok")
+                return
             with open(file_path, "r") as f:
                 content = f.read()  # f is out of scope in go_ahead()
                 def go_ahead():
@@ -2283,6 +2291,9 @@ class PaintApp(App[None]):
         def handle_selected_file_path(file_path: str) -> None:
             # TODO: DRY error handling with open_from_file_path
             try:
+                if os.path.getsize(file_path) > MAX_FILE_SIZE:
+                    self.message_box(_("Paste"), _("The file is too large to open."), "ok")
+                    return
                 with open(file_path, "r") as f:
                     self.paste(f.read())
                 window.close()