diff --git a/apps/web/src/browser/BrowserDeviceToolbar.browser.test.tsx b/apps/web/src/browser/BrowserDeviceToolbar.browser.test.tsx
new file mode 100644
index 0000000000000..65b58b6c4f683
--- /dev/null
+++ b/apps/web/src/browser/BrowserDeviceToolbar.browser.test.tsx
@@ -0,0 +1,71 @@
+import type { PreviewViewportSetting } from "@t3tools/contracts";
+import { useState } from "react";
+import { expect, it } from "vite-plus/test";
+import { userEvent } from "vite-plus/test/browser";
+
+import { render } from "../../test/render";
+import { BrowserDeviceToolbar } from "./BrowserDeviceToolbar";
+
+function Viewport({ width = 1920, height = 1080 }: { width?: number; height?: number }) {
+  const [setting, setSetting] = useState<PreviewViewportSetting>({
+    _tag: "freeform",
+    width,
+    height,
+  });
+  const [aspectRatio, setAspectRatio] = useState<number | null>(width / height);
+  if (setting._tag === "fill") throw new Error("Expected fixed viewport");
+  return (
+    <>
+      <BrowserDeviceToolbar
+        setting={setting}
+        width={800}
+        aspectRatio={aspectRatio}
+        onAspectRatioChange={setAspectRatio}
+        onChange={async (next) => setSetting(next)}
+      />
+      <output aria-label="Saved viewport">
+        {setting.width} × {setting.height}
+      </output>
+      <button type="button">Leave toolbar</button>
+    </>
+  );
+}
+
+it.each([
+  { width: 1920, height: 1080, axis: "width", typed: "2560", expected: "2560 × 1440" },
+  { width: 390, height: 844, axis: "height", typed: "2532", expected: "1170 × 2532" },
+])("keeps each typed $axis digit until the locked size is committed", async (testCase) => {
+  await using screen = await render(<Viewport {...testCase} />);
+  const input = screen.getByRole("spinbutton", { name: `Viewport ${testCase.axis}` });
+  await userEvent.clear(input);
+  await userEvent.type(input, testCase.typed);
+  await expect.element(input).toHaveValue(Number(testCase.typed));
+  await screen.getByRole("button", { name: "Leave toolbar" }).click();
+  await expect
+    .element(screen.getByRole("status", { name: "Saved viewport" }))
+    .toHaveTextContent(testCase.expected);
+});
+
+it("clamps a completed width below the locked minimum when leaving the toolbar", async () => {
+  await using screen = await render(<Viewport />);
+  const input = screen.getByRole("spinbutton", { name: "Viewport width" });
+  await userEvent.clear(input);
+  await userEvent.type(input, "256");
+  await expect.element(input).toHaveValue(256);
+  await screen.getByRole("button", { name: "Leave toolbar" }).click();
+  await expect
+    .element(screen.getByRole("status", { name: "Saved viewport" }))
+    .toHaveTextContent("427 × 240");
+});
+
+it("still limits a completed locked size to the viewport area cap", async () => {
+  await using screen = await render(<Viewport width={1920} height={1920} />);
+  const input = screen.getByRole("spinbutton", { name: "Viewport width" });
+  await userEvent.clear(input);
+  await userEvent.type(input, "3840");
+  await expect.element(input).toHaveValue(3840);
+  await screen.getByRole("button", { name: "Leave toolbar" }).click();
+  await expect
+    .element(screen.getByRole("status", { name: "Saved viewport" }))
+    .toHaveTextContent("2880 × 2880");
+});
diff --git a/apps/web/src/browser/BrowserDeviceToolbar.tsx b/apps/web/src/browser/BrowserDeviceToolbar.tsx
index fbd843c8d43fd..a880b3e42efe8 100644
--- a/apps/web/src/browser/BrowserDeviceToolbar.tsx
+++ b/apps/web/src/browser/BrowserDeviceToolbar.tsx
@@ -51,6 +51,7 @@ export function BrowserDeviceToolbar({
   const [customSize, setCustomSize] = useState<{
     readonly width: string;
     readonly height: string;
+    readonly axis?: "width" | "height";
   } | null>(null);
   const presentedSize = customSize ?? {
     width: String(setting.width),
@@ -61,15 +62,25 @@ export function BrowserDeviceToolbar({
     PREVIEW_VIEWPORT_PRESETS.some((preset) => preset.id === setting.presetId)
       ? setting.presetId
       : RESPONSIVE_VALUE;
-  const customWidth = Number(presentedSize.width);
-  const customHeight = Number(presentedSize.height);
+  const typedWidth = Number(presentedSize.width);
+  const typedHeight = Number(presentedSize.height);
+  const { width: customWidth, height: customHeight } =
+    aspectRatio === null || customSize?.axis === undefined
+      ? { width: typedWidth, height: typedHeight }
+      : resizeFreeformViewport(
+          { width: typedWidth, height: typedHeight },
+          { x: 0, y: 0 },
+          1,
+          customSize?.axis === "height" ? "south" : "east",
+          aspectRatio,
+        );
   const customValid =
-    Number.isInteger(customWidth) &&
-    Number.isInteger(customHeight) &&
-    customWidth >= PREVIEW_VIEWPORT_MIN_DIMENSION &&
-    customWidth <= PREVIEW_VIEWPORT_MAX_DIMENSION &&
-    customHeight >= PREVIEW_VIEWPORT_MIN_DIMENSION &&
-    customHeight <= PREVIEW_VIEWPORT_MAX_DIMENSION &&
+    Number.isInteger(typedWidth) &&
+    Number.isInteger(typedHeight) &&
+    typedWidth >= PREVIEW_VIEWPORT_MIN_DIMENSION &&
+    typedWidth <= PREVIEW_VIEWPORT_MAX_DIMENSION &&
+    typedHeight >= PREVIEW_VIEWPORT_MIN_DIMENSION &&
+    typedHeight <= PREVIEW_VIEWPORT_MAX_DIMENSION &&
     customWidth * customHeight <= PREVIEW_VIEWPORT_MAX_AREA;
 
   const apply = (next: PreviewViewportSetting, nextAspectRatio = aspectRatio) => {
@@ -96,6 +107,7 @@ export function BrowserDeviceToolbar({
       const next = {
         width: axis === "width" ? value : (current?.width ?? String(setting.width)),
         height: axis === "height" ? value : (current?.height ?? String(setting.height)),
+        axis,
       };
       const numeric = Number(value);
       if (
@@ -115,7 +127,11 @@ export function BrowserDeviceToolbar({
         axis === "width" ? "east" : "south",
         aspectRatio,
       );
-      return { width: String(resized.width), height: String(resized.height) };
+      return {
+        ...next,
+        width: axis === "width" ? value : String(resized.width),
+        height: axis === "height" ? value : String(resized.height),
+      };
     });
   };