diff --git a/emcclib.js b/emcclib.js
index 274da30..88ca4ac 100644
--- a/emcclib.js
+++ b/emcclib.js
@@ -188,22 +188,18 @@ mergeInto(LibraryManager.library, {
      * void js_activate_timer();
      *
      * Start calling the C timer_callback() function every frame.
+     * The C code ensures that the activate and deactivate functions
+     * are called in a sensible order.
      */
     js_activate_timer: function() {
-        if (!timer_active) {
-            timer_reference = performance.now();
-            var frame = function(now) {
-                timer = null;
-                timer_callback((now - timer_reference) / 1000.0);
-                /* The callback may have deactivated the timer. */
-                if (timer_active) {
-                    timer_reference = now;
-                    timer = window.requestAnimationFrame(frame);
-                }
-            }
-            timer_active = true;
+        timer_reference = performance.now();
+        var frame = function(now) {
             timer = window.requestAnimationFrame(frame);
-        }
+            // The callback might call js_deactivate_timer() below.
+            timer_callback((now - timer_reference) / 1000.0);
+            timer_reference = now;
+        };
+        timer = window.requestAnimationFrame(frame);
     },
 
     /*
@@ -212,13 +208,7 @@ mergeInto(LibraryManager.library, {
      * Stop calling the C timer_callback() function every frame.
      */
     js_deactivate_timer: function() {
-        if (timer_active) {
-            timer_active = false;
-            if (timer !== null) {
-                window.cancelAnimationFrame(timer);
-                timer = null;
-            }
-        }
+        window.cancelAnimationFrame(timer);
     },
 
     /*
diff --git a/emccpre.js b/emccpre.js
index 16833f5..666d37d 100644
--- a/emccpre.js
+++ b/emccpre.js
@@ -90,8 +90,7 @@ var midpoint_test_str = "ABCDEFGHIKLMNOPRSTUVWXYZ0123456789";
 var midpoint_cache = [];
 
 // Variables used by js_activate_timer() and js_deactivate_timer().
-var timer = null;
-var timer_active = false;
+var timer;
 var timer_reference;
 
 // void timer_callback(double tplus);