diff --git a/game.scm b/game.scm
index eb5f005..fe28a30 100644
--- a/game.scm
+++ b/game.scm
@@ -570,11 +570,19 @@
   (let* ((time (/ time 1000.0))
          (dt (- time *frame-time*)))
     (set! *frame-time* time)
-    (update-animation anim:player dt)
-    (update-animation anim:electron-head dt)
-    (update-animation anim:electron-tail dt)
-    (update-animation anim:gem dt)
-    (update-animation anim:ghost-gem dt)
+    ;; Prevent SUPER SPEED animations when the user switches away from
+    ;; the browser for awhile.  To my surprise,
+    ;; blur/focus/visibilitychanged events *DO NOT* trigger when the
+    ;; user switches to another program window, at least on my
+    ;; machine, so they are useless to prevent this problem.  Instead,
+    ;; we hack: Don't update animations if dt is unreasonably high,
+    ;; for some definition of unreasonable.
+    (unless (> dt 0.2)
+      (update-animation anim:player dt)
+      (update-animation anim:electron-head dt)
+      (update-animation anim:electron-tail dt)
+      (update-animation anim:gem dt)
+      (update-animation anim:ghost-gem dt))
     (clear-rect context 0.0 0.0 *canvas-width* *canvas-height*)
     (set-transform! context 1.0 0.0 0.0 1.0 0.0 0.0)
     (scale! context *canvas-scale* *canvas-scale*)