diff --git a/packages/node/src/integrations/context.ts b/packages/node/src/integrations/context.ts
index 73fa8fa40c03..c0991720d76e 100644
--- a/packages/node/src/integrations/context.ts
+++ b/packages/node/src/integrations/context.ts
@@ -189,10 +189,20 @@ function getAppContext(): AppContext {
   return { app_start_time, app_memory };
 }
 
-function getDeviceContext(deviceOpt: DeviceContextOptions | true): DeviceContext {
+/**
+ * Gets device information from os
+ */
+export function getDeviceContext(deviceOpt: DeviceContextOptions | true): DeviceContext {
   const device: DeviceContext = {};
 
-  device.boot_time = new Date(Date.now() - os.uptime() * 1000).toISOString();
+  // os.uptime or its return value seem to be undefined in certain environments (e.g. Azure functions).
+  // Hence, we only set boot time, if we get a valid uptime value.
+  // @see https://github.com/getsentry/sentry-javascript/issues/5856
+  const uptime = os.uptime && os.uptime();
+  if (typeof uptime === 'number') {
+    device.boot_time = new Date(Date.now() - uptime * 1000).toISOString();
+  }
+
   device.arch = os.arch();
 
   if (deviceOpt === true || deviceOpt.memory) {
diff --git a/packages/node/test/integrations/context.test.ts b/packages/node/test/integrations/context.test.ts
new file mode 100644
index 000000000000..519e101187ff
--- /dev/null
+++ b/packages/node/test/integrations/context.test.ts
@@ -0,0 +1,22 @@
+import * as os from 'os';
+
+import { getDeviceContext } from '../../src/integrations/context';
+
+describe('Context', () => {
+  describe('getDeviceContext', () => {
+    afterAll(() => {
+      jest.clearAllMocks();
+    });
+
+    it('returns boot time if os.uptime is defined and returns a valid uptime', () => {
+      const deviceCtx = getDeviceContext({});
+      expect(deviceCtx.boot_time).toEqual(expect.any(String));
+    });
+
+    it('returns no boot time if os.uptime() returns undefined', () => {
+      jest.spyOn(os, 'uptime').mockReturnValue(undefined as unknown as number);
+      const deviceCtx = getDeviceContext({});
+      expect(deviceCtx.boot_time).toBeUndefined();
+    });
+  });
+});