diff --git a/emcclib.js b/emcclib.js
index 60dbbf9..cee6d85 100644
--- a/emcclib.js
+++ b/emcclib.js
@@ -574,6 +574,12 @@ mergeInto(LibraryManager.library, {
      * alone and return false.
      */
     js_canvas_get_preferred_size: function(wp, hp) {
+        if (document.readyState == "complete" && containing_div !== null) {
+            var dpr = window.devicePixelRatio || 1;
+            setValue(wp, containing_div.clientWidth * dpr, "i32");
+            setValue(hp, containing_div.clientHeight * dpr, "i32");
+            return true;
+        }
         return false;
     },
 
@@ -591,6 +597,12 @@ mergeInto(LibraryManager.library, {
         if (resizable_div !== null)
             resizable_div.style.width =
                 w / (window.devicePixelRatio || 1) + "px";
+        else {
+            onscreen_canvas.style.width =
+                w / (window.devicePixelRatio || 1) + "px";
+            onscreen_canvas.style.height =
+                h / (window.devicePixelRatio || 1) + "px";
+        }
 
         onscreen_canvas.height = h;
         offscreen_canvas.height = h;
diff --git a/emccpre.js b/emccpre.js
index f7e0cc5..318f799 100644
--- a/emccpre.js
+++ b/emccpre.js
@@ -144,6 +144,10 @@ var undo_button, redo_button;
 // for positioning the resize handle.
 var resizable_div;
 
+// Alternatively, an extrinsically sized div that we will size the
+// puzzle to fit.
+var containing_div;
+
 // Helper function to find the absolute position of a given DOM
 // element on a page, by iterating upwards through the DOM finding
 // each element's offset from its parent, and thus calculating the
@@ -659,6 +663,24 @@ function initPuzzle() {
         rescale_puzzle();
     }
 
+    /*
+     * If the puzzle is sized to fit the page, try to detect changes
+     * of size of the containing element.  Ideally this would use a
+     * ResizeObserver on the containing_div, but I want this to work
+     * on KaiOS 2.5, which doesn't have ResizeObserver.  Instead we
+     * watch events that might indicate that the div has changed size.
+     */
+    containing_div = document.getElementById("puzzlecanvascontain");
+    if (containing_div !== null) {
+        var resize_handler = function(event) {
+            rescale_puzzle();
+        }
+        window.addEventListener("resize", resize_handler);
+        // Also catch the point when the document finishes loading,
+        // since sometimes we seem to get the div's size too early.
+        window.addEventListener("load", resize_handler);
+    }
+
     Module.preRun = function() {
         // Merge environment variables from HTML script element.
         // This means you can add something like this to the HTML: