diff --git a/Libraries/LibWeb/HTML/Navigable.h b/Libraries/LibWeb/HTML/Navigable.h
index 83e2340975..db780500e3 100644
--- a/Libraries/LibWeb/HTML/Navigable.h
+++ b/Libraries/LibWeb/HTML/Navigable.h
@@ -172,6 +172,8 @@ public:
     void set_viewport_size(CSSPixelSize);
     void perform_scroll_of_viewport_scrolling_box(CSSPixelPoint position);
 
+    Painting::BackingStoreManager& backing_store_manager() { return *m_backing_store_manager; }
+
     // https://html.spec.whatwg.org/multipage/webappapis.html#rendering-opportunity
     [[nodiscard]] bool has_a_rendering_opportunity() const;
 
diff --git a/Libraries/LibWeb/Internals/Internals.cpp b/Libraries/LibWeb/Internals/Internals.cpp
index 4f09080421..0d11b01635 100644
--- a/Libraries/LibWeb/Internals/Internals.cpp
+++ b/Libraries/LibWeb/Internals/Internals.cpp
@@ -437,6 +437,11 @@ void Internals::set_browser_zoom(double factor)
     page().client().page_did_set_browser_zoom(factor);
 }
 
+void Internals::set_device_pixel_ratio(double ratio)
+{
+    page().client().page_did_set_device_pixel_ratio_for_testing(ratio);
+}
+
 bool Internals::headless()
 {
     return page().client().is_headless();
diff --git a/Libraries/LibWeb/Internals/Internals.h b/Libraries/LibWeb/Internals/Internals.h
index 69824a6604..d83b04d346 100644
--- a/Libraries/LibWeb/Internals/Internals.h
+++ b/Libraries/LibWeb/Internals/Internals.h
@@ -69,6 +69,7 @@ public:
     static void set_echo_server_port(u16 port);
 
     void set_browser_zoom(double factor);
+    void set_device_pixel_ratio(double ratio);
 
     bool headless();
 
diff --git a/Libraries/LibWeb/Internals/Internals.idl b/Libraries/LibWeb/Internals/Internals.idl
index e164be6ace..344ef87248 100644
--- a/Libraries/LibWeb/Internals/Internals.idl
+++ b/Libraries/LibWeb/Internals/Internals.idl
@@ -58,6 +58,7 @@ interface Internals {
     unsigned short getEchoServerPort();
 
     undefined setBrowserZoom(double factor);
+    undefined setDevicePixelRatio(double ratio);
 
     readonly attribute boolean headless;
 
diff --git a/Libraries/LibWeb/Page/Page.h b/Libraries/LibWeb/Page/Page.h
index c1df05e7c2..00114d71b1 100644
--- a/Libraries/LibWeb/Page/Page.h
+++ b/Libraries/LibWeb/Page/Page.h
@@ -417,6 +417,7 @@ public:
     virtual void page_did_receive_test_variant_metadata(JsonValue) { }
 
     virtual void page_did_set_browser_zoom([[maybe_unused]] double factor) { }
+    virtual void page_did_set_device_pixel_ratio_for_testing([[maybe_unused]] double ratio) { }
 
     virtual void page_did_change_theme_color(Gfx::Color) { }
 
diff --git a/Services/WebContent/PageClient.cpp b/Services/WebContent/PageClient.cpp
index 26d23f9a08..3f8ccf433d 100644
--- a/Services/WebContent/PageClient.cpp
+++ b/Services/WebContent/PageClient.cpp
@@ -24,6 +24,7 @@
 #include <LibWeb/HTML/HTMLLinkElement.h>
 #include <LibWeb/HTML/Scripting/ClassicScript.h>
 #include <LibWeb/HTML/TraversableNavigable.h>
+#include <LibWeb/InvalidateDisplayList.h>
 #include <LibWeb/Layout/Viewport.h>
 #include <LibWeb/Painting/PaintableBox.h>
 #include <LibWebView/SiteIsolation.h>
@@ -207,6 +208,23 @@ void PageClient::set_viewport_size(Web::DevicePixelSize const& size)
     page().top_level_traversable()->set_viewport_size(page().device_to_css_size(size));
 }
 
+void PageClient::set_device_pixel_ratio(double device_pixel_ratio)
+{
+    if (m_device_pixel_ratio == device_pixel_ratio)
+        return;
+
+    m_device_pixel_ratio = device_pixel_ratio;
+
+    auto traversable = page().top_level_traversable();
+    traversable->backing_store_manager()
+        .resize_backing_stores_if_needed(Web::Painting::BackingStoreManager::WindowResizingInProgress::No);
+
+    if (auto document = traversable->active_document()) {
+        document->set_needs_media_query_evaluation();
+        document->set_needs_display(Web::InvalidateDisplayList::Yes);
+    }
+}
+
 void PageClient::set_maximum_frames_per_second(u64 maximum_frames_per_second)
 {
     m_maximum_frames_per_second = maximum_frames_per_second;
@@ -372,6 +390,11 @@ void PageClient::page_did_set_browser_zoom(double factor)
     }));
 }
 
+void PageClient::page_did_set_device_pixel_ratio_for_testing(double ratio)
+{
+    set_device_pixel_ratio(ratio);
+}
+
 void PageClient::page_did_request_context_menu(Web::CSSPixelPoint content_position)
 {
     client().async_did_request_context_menu(m_id, page().css_to_device_point(content_position).to_type<int>());
diff --git a/Services/WebContent/PageClient.h b/Services/WebContent/PageClient.h
index 5fb158a7f8..8d4d5b4baa 100644
--- a/Services/WebContent/PageClient.h
+++ b/Services/WebContent/PageClient.h
@@ -58,7 +58,7 @@ public:
         m_all_screen_rects = rects;
         m_main_screen_index = main_screen_index;
     }
-    void set_device_pixel_ratio(double device_pixel_ratio) { m_device_pixel_ratio = device_pixel_ratio; }
+    void set_device_pixel_ratio(double device_pixel_ratio);
     void set_zoom_level(double zoom_level) { m_zoom_level = zoom_level; }
     void set_maximum_frames_per_second(u64 maximum_frames_per_second);
     void set_preferred_color_scheme(Web::CSS::PreferredColorScheme);
@@ -182,6 +182,7 @@ private:
     virtual void page_did_receive_reference_test_metadata(JsonValue) override;
     virtual void page_did_receive_test_variant_metadata(JsonValue) override;
     virtual void page_did_set_browser_zoom(double factor) override;
+    virtual void page_did_set_device_pixel_ratio_for_testing(double ratio) override;
     virtual void page_did_change_theme_color(Gfx::Color color) override;
     virtual void page_did_insert_clipboard_entry(Web::Clipboard::SystemClipboardRepresentation const&, StringView presentation_style) override;
     virtual void page_did_request_clipboard_entries(u64 request_id) override;
diff --git a/Tests/LibWeb/Text/expected/device-pixel-ratio-media-query.txt b/Tests/LibWeb/Text/expected/device-pixel-ratio-media-query.txt
new file mode 100644
index 0000000000..6bd45c7259
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/device-pixel-ratio-media-query.txt
@@ -0,0 +1,5 @@
+Initial matches (at 1x): false
+Change event 1: matches = true
+PASS: Media query matched after DPI changed to 2x
+Change event 2: matches = false
+PASS: Media query unmatched after DPI changed back to 1x
diff --git a/Tests/LibWeb/Text/input/device-pixel-ratio-media-query.html b/Tests/LibWeb/Text/input/device-pixel-ratio-media-query.html
new file mode 100644
index 0000000000..70549c2953
--- /dev/null
+++ b/Tests/LibWeb/Text/input/device-pixel-ratio-media-query.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<script src="include.js"></script>
+<script>
+    asyncTest(done => {
+        const mql = window.matchMedia("(resolution: 2dppx)");
+        println(`Initial matches (at 1x): ${mql.matches}`);
+
+        let changeCount = 0;
+
+        mql.addEventListener("change", (event) => {
+            changeCount++;
+            println(`Change event ${changeCount}: matches = ${event.matches}`);
+
+            if (changeCount === 1) {
+                // First change: 1x -> 2x, should now match.
+                if (event.matches) {
+                    println("PASS: Media query matched after DPI changed to 2x");
+                } else {
+                    println("FAIL: Media query should match at 2x DPI");
+                }
+                internals.setDevicePixelRatio(1);
+            } else if (changeCount === 2) {
+                // Second change: 2x -> 1x, should no longer match.
+                if (!event.matches) {
+                    println("PASS: Media query unmatched after DPI changed back to 1x");
+                } else {
+                    println("FAIL: Media query should not match at 1x DPI");
+                }
+                done();
+            }
+        });
+
+        // Change to 2x DPI - this should trigger the first change event.
+        internals.setDevicePixelRatio(2);
+    });
+</script>