diff --git a/src/Magnum/Platform/EmscriptenApplication.cpp b/src/Magnum/Platform/EmscriptenApplication.cpp
index cefbc8c5f..f38e6525d 100644
--- a/src/Magnum/Platform/EmscriptenApplication.cpp
+++ b/src/Magnum/Platform/EmscriptenApplication.cpp
@@ -389,12 +389,35 @@ void EmscriptenApplication::setContainerCssClass(const std::string& cssClass) {
     #pragma GCC diagnostic ignored "-Wdollar-in-identifier-extension"
     EM_ASM_({document.getElementById('container').className = AsciiToString($0);}, cssClass.data());
     #pragma GCC diagnostic pop
+
+    /* Trigger a potential viewport event -- we don't poll the canvas size like
+       Sdl2Application does, so it needs to be done explicitly */
+    handleCanvasResize(nullptr);
 }
 
 void EmscriptenApplication::swapBuffers() {
     emscripten_webgl_commit_frame();
 }
 
+/* Called from window resize event but also explicitly from
+   setContainerCssClass() */
+void EmscriptenApplication::handleCanvasResize(const EmscriptenUiEvent* event) {
+    /* See windowSize() for why we hardcode "#canvas" here */
+    const Vector2i canvasSize{windowSize()};
+    if(canvasSize != _lastKnownCanvasSize) {
+        _lastKnownCanvasSize = canvasSize;
+        const Vector2i size = canvasSize*_dpiScaling*_devicePixelRatio;
+        emscripten_set_canvas_element_size("#canvas", size.x(), size.y());
+        ViewportEvent e{event, canvasSize,
+            #ifdef MAGNUM_TARGET_GL
+            framebufferSize(),
+            #endif
+            _dpiScaling, _devicePixelRatio};
+        viewportEvent(e);
+        _flags |= Flag::Redraw;
+    }
+}
+
 void EmscriptenApplication::setupCallbacks(bool resizable) {
     /* Since 1.38.17 all emscripten_set_*_callback() are macros. Play it safe
        and wrap all lambdas in () to avoid the preprocessor getting upset when
@@ -413,20 +436,7 @@ void EmscriptenApplication::setupCallbacks(bool resizable) {
         #endif
         auto cb = [](int, const EmscriptenUiEvent* event, void* userData) -> Int {
             EmscriptenApplication& app = *static_cast<EmscriptenApplication*>(userData);
-            /* See windowSize() for why we hardcode "#canvas" here */
-            const Vector2i canvasSize{app.windowSize()};
-            if(canvasSize != app._lastKnownCanvasSize) {
-                app._lastKnownCanvasSize = canvasSize;
-                const Vector2i size = canvasSize*app._dpiScaling*app._devicePixelRatio;
-                emscripten_set_canvas_element_size("#canvas", size.x(), size.y());
-                ViewportEvent e{*event, canvasSize,
-                    #ifdef MAGNUM_TARGET_GL
-                    app.framebufferSize(),
-                    #endif
-                    app._dpiScaling, app._devicePixelRatio};
-                app.viewportEvent(e);
-                app._flags |= Flag::Redraw;
-            }
+            app.handleCanvasResize(event);
             return false; /** @todo what does ignoring a resize event mean? */
         };
         emscripten_set_resize_callback(target, this, false, cb);
diff --git a/src/Magnum/Platform/EmscriptenApplication.h b/src/Magnum/Platform/EmscriptenApplication.h
index 9aa595c23..4f2fc142e 100644
--- a/src/Magnum/Platform/EmscriptenApplication.h
+++ b/src/Magnum/Platform/EmscriptenApplication.h
@@ -624,6 +624,7 @@ class EmscriptenApplication {
 
         CORRADE_ENUMSET_FRIEND_OPERATORS(Flags)
 
+        void handleCanvasResize(const EmscriptenUiEvent* event);
         /* Sorry, but can't use Configuration::WindowFlags here :( */
         void setupCallbacks(bool resizable);
         void setupAnimationFrame(bool ForceAnimationFrame);
@@ -1050,13 +1051,19 @@ class EmscriptenApplication::ViewportEvent {
          */
         Vector2 devicePixelRatio() const { return _devicePixelRatio; }
 
-        /** @brief Underlying Emscripten event */
-        const EmscriptenUiEvent& event() const { return _event; }
+        /**
+         * @brief Underlying Emscripten event
+         *
+         * If the viewport event doesn't come from a browser event (for example
+         * when the canvas was resized programatically and not as a consequence
+         * of window size change), the function returns @cpp nullptr @ce.
+         */
+        const EmscriptenUiEvent* event() const { return _event; }
 
     private:
         friend EmscriptenApplication;
 
-        explicit ViewportEvent(const EmscriptenUiEvent& event,
+        explicit ViewportEvent(const EmscriptenUiEvent* event,
             const Vector2i& windowSize,
             #ifdef MAGNUM_TARGET_GL
             const Vector2i& framebufferSize,
@@ -1069,7 +1076,7 @@ class EmscriptenApplication::ViewportEvent {
                 #endif
                 _dpiScaling{dpiScaling}, _devicePixelRatio{devicePixelRatio} {}
 
-        const EmscriptenUiEvent& _event;
+        const EmscriptenUiEvent* _event;
         const Vector2i _windowSize;
         #ifdef MAGNUM_TARGET_GL
         const Vector2i _framebufferSize;