diff --git a/packages/analytics-browser/src/gtm-snippet-index.ts b/packages/analytics-browser/src/gtm-snippet-index.ts
index 3e47b409b..a5ad62d7d 100644
--- a/packages/analytics-browser/src/gtm-snippet-index.ts
+++ b/packages/analytics-browser/src/gtm-snippet-index.ts
@@ -27,12 +27,20 @@ import { runQueuedFunctions } from './utils/snippet-helper';
     createInstance: createNamedInstance,
   });
 
+  // Normalize proxy queues so a pre-existing global with `invoked = true` but
+  // missing `_q` / `_iq` doesn't crash either this bootstrap or downstream
+  // GTM wrapper code that reads `amplitudeGTM._iq[name]` directly.
+  GlobalScope.amplitudeGTM._q = GlobalScope.amplitudeGTM._q || [];
+  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+  // @ts-ignore
+  GlobalScope.amplitudeGTM._iq = GlobalScope.amplitudeGTM._iq || {};
+
   if (GlobalScope.amplitudeGTM.invoked) {
     const queue = GlobalScope.amplitudeGTM._q;
     GlobalScope.amplitudeGTM._q = [];
     runQueuedFunctions(amplitudeGTM, queue);
 
-    const instanceNames = Object.keys(GlobalScope.amplitudeGTM._iq) || [];
+    const instanceNames = Object.keys(GlobalScope.amplitudeGTM._iq);
     for (let i = 0; i < instanceNames.length; i++) {
       const instanceName = instanceNames[i];
       const instance = Object.assign(GlobalScope.amplitudeGTM._iq[instanceName], createNamedInstance(instanceName));
diff --git a/packages/analytics-browser/src/snippet-index.ts b/packages/analytics-browser/src/snippet-index.ts
index d85b2481d..58c3b90bf 100644
--- a/packages/analytics-browser/src/snippet-index.ts
+++ b/packages/analytics-browser/src/snippet-index.ts
@@ -44,12 +44,20 @@ function resolveCurrentScriptUrl(): string | undefined {
     createInstance: createNamedInstance,
   });
 
+  // Normalize proxy queues so a pre-existing global with `invoked = true` but
+  // missing `_q` / `_iq` doesn't crash either this bootstrap or downstream
+  // code (e.g. GTM wrappers that read `amplitude._iq[name]` directly).
+  GlobalScope.amplitude._q = GlobalScope.amplitude._q || [];
+  // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+  // @ts-ignore
+  GlobalScope.amplitude._iq = GlobalScope.amplitude._iq || {};
+
   if (GlobalScope.amplitude.invoked) {
     const queue = GlobalScope.amplitude._q;
     GlobalScope.amplitude._q = [];
     runQueuedFunctions(amplitude, queue);
 
-    const instanceNames = Object.keys(GlobalScope.amplitude._iq) || [];
+    const instanceNames = Object.keys(GlobalScope.amplitude._iq);
     for (let i = 0; i < instanceNames.length; i++) {
       const instanceName = instanceNames[i];
       const instance = Object.assign(GlobalScope.amplitude._iq[instanceName], createNamedInstance(instanceName));
diff --git a/packages/analytics-browser/src/utils/snippet-helper.ts b/packages/analytics-browser/src/utils/snippet-helper.ts
index 9a0b67363..ed3fd4920 100644
--- a/packages/analytics-browser/src/utils/snippet-helper.ts
+++ b/packages/analytics-browser/src/utils/snippet-helper.ts
@@ -17,7 +17,7 @@ interface InstanceProxy {
  * Applies the proxied functions on the proxied amplitude snippet to an instance of the real object.
  * @ignore
  */
-export const runQueuedFunctions = (instance: object, queue: QueueProxy) => {
+export const runQueuedFunctions = (instance: object, queue: QueueProxy | undefined) => {
   convertProxyObjectToRealObject(instance, queue);
 };
 
@@ -25,7 +25,10 @@ export const runQueuedFunctions = (instance: object, queue: QueueProxy) => {
  * Applies the proxied functions on the proxied object to an instance of the real object.
  * Used to convert proxied Identify and Revenue objects.
  */
-export const convertProxyObjectToRealObject = <T>(instance: T, queue: QueueProxy): T => {
+export const convertProxyObjectToRealObject = <T>(instance: T, queue: QueueProxy | undefined): T => {
+  if (!queue) {
+    return instance;
+  }
   for (let i = 0; i < queue.length; i++) {
     const { name, args, resolve } = queue[i];
     const fn = instance && instance[name as keyof T];
diff --git a/packages/analytics-browser/test/utils/snippet-helper.test.ts b/packages/analytics-browser/test/utils/snippet-helper.test.ts
index c6f6cbe0b..e435fa102 100644
--- a/packages/analytics-browser/test/utils/snippet-helper.test.ts
+++ b/packages/analytics-browser/test/utils/snippet-helper.test.ts
@@ -47,5 +47,11 @@ describe('snippet-helper', () => {
       expect(SnippetHelper.convertProxyObjectToRealObject(instance, queue)).toBe(instance);
       expect(resolve).toHaveBeenCalledTimes(1);
     });
+
+    test('should return instance when queue is undefined', () => {
+      const instance = { init: jest.fn() };
+      expect(SnippetHelper.convertProxyObjectToRealObject(instance, undefined)).toBe(instance);
+      expect(instance.init).not.toHaveBeenCalled();
+    });
   });
 });