diff --git a/.changeset/uplot-posix-locale.md b/.changeset/uplot-posix-locale.md
new file mode 100644
index 0000000000..2b502a2829
--- /dev/null
+++ b/.changeset/uplot-posix-locale.md
@@ -0,0 +1,5 @@
+---
+'@hyperdx/app': patch
+---
+
+fix: The app no longer crashes on load in browsers that report a POSIX-style language such as `en-US@posix`
diff --git a/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch b/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch
new file mode 100644
index 0000000000..80a885b116
--- /dev/null
+++ b/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch
@@ -0,0 +1,40 @@
+diff --git a/dist/uPlot.cjs.js b/dist/uPlot.cjs.js
+index 98b7582dff68d4f4d9e0068cc77bec9d33ea4904..d137fbcb9f24358d7e59350907181106fc5b231d 100644
+--- a/dist/uPlot.cjs.js
++++ b/dist/uPlot.cjs.js
+@@ -441,7 +441,14 @@ function _rangeNum(_min, _max, cfg) {
+ }
+ 
+ // alternative: https://stackoverflow.com/a/2254896
+-const numFormatter = new Intl.NumberFormat(domEnv ? nav.language : 'en-US');
++// Patched: Intl rejects POSIX-style tags such as 'en-US@posix', which some
++// browsers report as navigator.language. Fall back instead of throwing at import.
++let numFormatter;
++try {
++	numFormatter = new Intl.NumberFormat(domEnv ? nav.language : 'en-US');
++} catch (e) {
++	numFormatter = new Intl.NumberFormat('en-US');
++}
+ const fmtNum = val => numFormatter.format(val);
+ 
+ const M = Math;
+diff --git a/dist/uPlot.esm.js b/dist/uPlot.esm.js
+index 87473c9cfb3366f57883cb803114a87c64d4b6b8..740bd3626a1f8bd6bbe352878e55e898e759784c 100644
+--- a/dist/uPlot.esm.js
++++ b/dist/uPlot.esm.js
+@@ -439,7 +439,14 @@ function _rangeNum(_min, _max, cfg) {
+ }
+ 
+ // alternative: https://stackoverflow.com/a/2254896
+-const numFormatter = new Intl.NumberFormat(domEnv ? nav.language : 'en-US');
++// Patched: Intl rejects POSIX-style tags such as 'en-US@posix', which some
++// browsers report as navigator.language. Fall back instead of throwing at import.
++let numFormatter;
++try {
++	numFormatter = new Intl.NumberFormat(domEnv ? nav.language : 'en-US');
++} catch (e) {
++	numFormatter = new Intl.NumberFormat('en-US');
++}
+ const fmtNum = val => numFormatter.format(val);
+ 
+ const M = Math;
diff --git a/packages/app/package.json b/packages/app/package.json
index 829742797e..101e226cce 100644
--- a/packages/app/package.json
+++ b/packages/app/package.json
@@ -100,7 +100,7 @@
     "store2": "^2.14.3",
     "strip-ansi": "^6.0.1",
     "timestamp-nano": "^1.0.1",
-    "uplot": "^1.6.31",
+    "uplot": "patch:uplot@npm%3A1.6.32#~/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch",
     "uplot-react": "^1.2.2",
     "zod": "3.25"
   },
diff --git a/packages/app/playwright.config.ts b/packages/app/playwright.config.ts
index 78524bd2f9..c5bca85edd 100644
--- a/packages/app/playwright.config.ts
+++ b/packages/app/playwright.config.ts
@@ -75,6 +75,9 @@ export default defineConfig({
     screenshot: 'only-on-failure',
     /* Record video on failure */
     video: 'retain-on-failure',
+    // Otherwise Chromium takes navigator.language from the host locale, so
+    // number and date formatting would vary between machines.
+    locale: 'en-US',
   },
 
   /* Global test timeout - CI needs more time than local */
diff --git a/packages/app/src/components/DBHeatmapChart/__tests__/uplotLocale.test.ts b/packages/app/src/components/DBHeatmapChart/__tests__/uplotLocale.test.ts
new file mode 100644
index 0000000000..d18b2f3ac9
--- /dev/null
+++ b/packages/app/src/components/DBHeatmapChart/__tests__/uplotLocale.test.ts
@@ -0,0 +1,23 @@
+// uPlot builds an Intl.NumberFormat from navigator.language at import time.
+// Chromium on LANG=C.UTF-8 hosts reports 'en-US@posix', which Intl rejects;
+// our yarn patch makes uPlot fall back to 'en-US' instead of throwing.
+describe('uplot locale patch', () => {
+  let languageSpy: jest.SpyInstance;
+
+  afterEach(() => {
+    languageSpy.mockRestore();
+  });
+
+  it('imports and formats numbers when navigator.language is not a valid BCP 47 tag', async () => {
+    languageSpy = jest
+      .spyOn(window.navigator, 'language', 'get')
+      .mockReturnValue('en-US@posix');
+
+    expect(() => new Intl.NumberFormat('en-US@posix')).toThrow(RangeError);
+
+    await jest.isolateModulesAsync(async () => {
+      const { default: uPlot } = await import('uplot');
+      expect(uPlot.fmtNum(1234.5)).toBe('1,234.5');
+    });
+  });
+});
diff --git a/packages/app/tests/e2e/global-setup-fullstack.ts b/packages/app/tests/e2e/global-setup-fullstack.ts
index 9c196b6900..a0c92624e7 100644
--- a/packages/app/tests/e2e/global-setup-fullstack.ts
+++ b/packages/app/tests/e2e/global-setup-fullstack.ts
@@ -145,7 +145,11 @@ async function globalSetup(_config: FullConfig) {
   console.log('Creating test user and logging in');
 
   const browser = await chromium.launch();
-  const context = await browser.newContext({ baseURL: APP_URL });
+  // Global setup doesn't inherit `use` from playwright.config.ts.
+  const context = await browser.newContext({
+    baseURL: APP_URL,
+    locale: 'en-US',
+  });
   const page = await context.newPage();
 
   try {
diff --git a/yarn.lock b/yarn.lock
index b7d3b4f74f..9cb5ded064 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -4977,7 +4977,7 @@ __metadata:
     timestamp-nano: "npm:^1.0.1"
     ts-jest: "npm:^29.4.11"
     typescript: "npm:^6.0.3"
-    uplot: "npm:^1.6.31"
+    uplot: "patch:uplot@npm%3A1.6.32#~/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch"
     uplot-react: "npm:^1.2.2"
     zod: "npm:3.25"
   languageName: unknown
@@ -30604,13 +30604,20 @@ __metadata:
   languageName: node
   linkType: hard
 
-"uplot@npm:^1.6.31":
+"uplot@npm:1.6.32":
   version: 1.6.32
   resolution: "uplot@npm:1.6.32"
   checksum: 10c0/4d9cdd5f53371656cfc178ea4ae0d8c9bdbe4c98c99df847926d7e5f5a5bcb8043561219da2979fee7616aabe3619d80fee093befdfe39aae65e6621284c39b1
   languageName: node
   linkType: hard
 
+"uplot@patch:uplot@npm%3A1.6.32#~/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch":
+  version: 1.6.32
+  resolution: "uplot@patch:uplot@npm%3A1.6.32#~/.yarn/patches/uplot-npm-1.6.32-350d2da00d.patch::version=1.6.32&hash=d25b41"
+  checksum: 10c0/8eac8ee3e294a2834f6295eea230bd6dba6c7031a0d67f79f02eacec15ceaada5e82accd9ef1b6462326ec35e9475779f072b9be7625550a3e2f1d8fc70d2470
+  languageName: node
+  linkType: hard
+
 "uri-js@npm:^4.2.2":
   version: 4.4.1
   resolution: "uri-js@npm:4.4.1"