diff --git a/src/__tests__/extensions/replay/config.test.ts b/src/__tests__/extensions/replay/config.test.ts
index 42f67c5f2..9f89b5840 100644
--- a/src/__tests__/extensions/replay/config.test.ts
+++ b/src/__tests__/extensions/replay/config.test.ts
@@ -216,6 +216,22 @@ describe('config', () => {
             })
         })
 
+        it('can amend the provided object', () => {
+            const posthogConfig = defaultConfig()
+            posthogConfig.session_recording.maskCapturedNetworkRequestFn = (data) => {
+                data.name = 'changed'
+                return data
+            }
+            const networkOptions = buildNetworkRequestOptions(posthogConfig, {})
+
+            const cleaned = networkOptions.maskRequestFn!({
+                name: 'something',
+            } as Partial<CapturedNetworkRequest> as CapturedNetworkRequest)
+            expect(cleaned).toEqual({
+                name: 'changed',
+            })
+        })
+
         it('should remove the Authorization header from requests even when a mask request fn is set', () => {
             const posthogConfig = defaultConfig()
             posthogConfig.session_recording.maskCapturedNetworkRequestFn = (data) => {
diff --git a/src/types.ts b/src/types.ts
index a1f729089..d037baa64 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -475,7 +475,12 @@ export type NetworkRequest = {
 //     readonly name: string;
 //     readonly startTime: DOMHighResTimeStamp;
 // NB: properties below here are ALPHA, don't rely on them, they may change without notice
-export type CapturedNetworkRequest = Omit<PerformanceEntry, 'toJSON'> & {
+
+// we mirror PerformanceEntry since we read into this type from a PerformanceObserver,
+// but we don't want to inherit its readonly-iness
+type Writable<T> = { -readonly [P in keyof T]: T[P] }
+
+export type CapturedNetworkRequest = Writable<Omit<PerformanceEntry, 'toJSON'>> & {
     // properties below here are ALPHA, don't rely on them, they may change without notice
     method?: string
     initiatorType?: InitiatorType