diff --git a/error-mode.fnl b/error-mode.fnl
new file mode 100644
index 0000000..3aed9d5
--- /dev/null
+++ b/error-mode.fnl
@@ -0,0 +1,30 @@
+;; This mode has two purposes:
+;; * display the stack trace that caused the error
+;; * allow the user to decide whether to retry after reloading or quit
+
+;; Since we can't know which module needs to be reloaded, we rely on the user
+;; doing a ,reload foo in the repl.
+
+(var state nil)
+
+(local explanation "Press escape to quit.
+Press space to return to the previous mode after reloading in the repl.")
+
+(fn draw []
+  (love.graphics.clear 0.34 0.61 0.86)
+  (love.graphics.setColor 0.9 0.9 0.9)
+  (love.graphics.print state.msg 10 10)
+  (love.graphics.print explanation 15 25)
+  (love.graphics.print state.traceback 15 50))
+
+(fn keypressed [key set-mode]
+  (match key
+    :escape (love.event.quit)
+    :space (set-mode state.old-mode)))
+
+(fn activate [old-mode msg traceback]
+  (print msg)
+  (print traceback)
+  (set state {: old-mode : msg : traceback}))
+
+{: draw : keypressed : activate}
diff --git a/wrap.fnl b/wrap.fnl
index e76ac1f..51284ec 100644
--- a/wrap.fnl
+++ b/wrap.fnl
@@ -1,37 +1,44 @@
-(local repl (require "lib.stdio"))
+(local fennel (require :lib.fennel))
+(local repl (require :lib.stdio))
 (local canvas (let [(w h) (love.window.getMode)]
                 (love.graphics.newCanvas w h)))
 
 (var scale 1)
 
 ;; set the first mode
-(var mode (require "mode-intro"))
+(var (mode mode-name) nil)
 
-(fn set-mode [mode-name ...]
-  (set mode (require mode-name))
+(fn set-mode [new-mode-name ...]
+  (set (mode mode-name) (values (require new-mode-name) new-mode-name))
   (when mode.activate
-    (mode.activate ...)))
+    (match (pcall mode.activate ...)
+      (false msg) (print mode-name "activate error" msg))))
 
 (fn love.load []
+  (set-mode :mode-intro)
   (canvas:setFilter "nearest" "nearest")
   (repl.start))
 
+(fn safely [f]
+  (xpcall f #(set-mode :error-mode mode-name $ (fennel.traceback))))
+
 (fn love.draw []
   ;; the canvas allows you to get sharp pixel-art style scaling; if you
   ;; don't want that, just skip that and call mode.draw directly.
   (love.graphics.setCanvas canvas)
   (love.graphics.clear)
   (love.graphics.setColor 1 1 1)
-  (mode.draw)
+  (safely mode.draw)
   (love.graphics.setCanvas)
   (love.graphics.setColor 1 1 1)
   (love.graphics.draw canvas 0 0 0 scale scale))
 
 (fn love.update [dt]
-  (mode.update dt set-mode))
+  (when mode.update
+    (safely #(mode.update dt set-mode))))
 
 (fn love.keypressed [key]
   (if (and (love.keyboard.isDown "lctrl" "rctrl" "capslock") (= key "q"))
       (love.event.quit)
       ;; add what each keypress should do in each mode
-      (mode.keypressed key set-mode)))
+      (safely #(mode.keypressed key set-mode))))