diff --git a/packages/react/src/hooks/useReactFlow.ts b/packages/react/src/hooks/useReactFlow.ts
index 2cfc3430..84b1cb77 100644
--- a/packages/react/src/hooks/useReactFlow.ts
+++ b/packages/react/src/hooks/useReactFlow.ts
@@ -8,6 +8,7 @@ import {
   isRectObject,
   NodeRemoveChange,
   nodeToRect,
+  withResolvers,
   type Rect,
 } from '@xyflow/system';
 
@@ -280,7 +281,7 @@ export function useReactFlow<NodeType extends Node = Node, EdgeType extends Edge
       fitView: async (options: FitViewOptions<NodeType> | undefined) => {
         // We either create a new Promise or reuse the existing one
         // Even if fitView is called multiple times in a row, we only end up with a single Promise
-        const fitViewResolver = store.getState().fitViewResolver ?? Promise.withResolvers<boolean>();
+        const fitViewResolver = store.getState().fitViewResolver ?? withResolvers<boolean>();
 
         // We schedule a fitView by setting fitViewQueued and triggering a setNodes
         store.setState({ fitViewQueued: true, fitViewOptions: options, fitViewResolver });
diff --git a/packages/react/src/types/store.ts b/packages/react/src/types/store.ts
index efd9d957..aef78aaa 100644
--- a/packages/react/src/types/store.ts
+++ b/packages/react/src/types/store.ts
@@ -1,5 +1,6 @@
 import {
   ConnectionMode,
+  withResolvers,
   type ConnectionState,
   type CoordinateExtent,
   type InternalNodeUpdate,
@@ -121,7 +122,7 @@ export type ReactFlowStore<NodeType extends Node = Node, EdgeType extends Edge =
 
   fitViewQueued: boolean;
   fitViewOptions: FitViewOptions | undefined;
-  fitViewResolver: PromiseWithResolvers<boolean> | null;
+  fitViewResolver: ReturnType<typeof withResolvers<boolean>> | null;
 
   onNodesDelete?: OnNodesDelete<NodeType>;
   onEdgesDelete?: OnEdgesDelete<EdgeType>;
diff --git a/packages/svelte/src/lib/store/index.ts b/packages/svelte/src/lib/store/index.ts
index 83c6c623..8f07f105 100644
--- a/packages/svelte/src/lib/store/index.ts
+++ b/packages/svelte/src/lib/store/index.ts
@@ -18,7 +18,8 @@ import {
   type UpdateConnection,
   type ConnectionState,
   type NodeOrigin,
-  updateAbsolutePositions
+  updateAbsolutePositions,
+  withResolvers
 } from '@xyflow/system';
 
 import type { EdgeTypes, NodeTypes, Node, Edge, FitViewOptions } from '$lib/types';
@@ -146,7 +147,7 @@ export function createStore({
   function fitView(options?: FitViewOptions) {
     // We either create a new Promise or reuse the existing one
     // Even if fitView is called multiple times in a row, we only end up with a single Promise
-    const fitViewResolver = get(store.fitViewResolver) ?? Promise.withResolvers<boolean>();
+    const fitViewResolver = get(store.fitViewResolver) ?? withResolvers<boolean>();
 
     // We schedule a fitView by setting fitViewQueued and triggering a setNodes
     store.fitViewQueued.set(true);
diff --git a/packages/svelte/src/lib/store/initial-store.ts b/packages/svelte/src/lib/store/initial-store.ts
index 3b0064a8..3a88696d 100644
--- a/packages/svelte/src/lib/store/initial-store.ts
+++ b/packages/svelte/src/lib/store/initial-store.ts
@@ -25,7 +25,8 @@ import {
   type EdgeLookup,
   type ConnectionState,
   type ParentLookup,
-  getInternalNodesBounds
+  getInternalNodesBounds,
+  withResolvers
 } from '@xyflow/system';
 
 import DefaultNode from '$lib/components/nodes/DefaultNode.svelte';
@@ -114,7 +115,7 @@ export const getInitialStore = ({
 
   const fitViewQueued = writable<boolean>(false);
   const fitViewOptions = writable<FitViewOptions | undefined>(undefined);
-  const fitViewResolver = writable<PromiseWithResolvers<boolean> | null>(null);
+  const fitViewResolver = writable<ReturnType<typeof withResolvers<boolean>> | null>(null);
   const panZoom = writable<PanZoomInstance | null>(null);
   const widthStore = writable<number>(500);
   const heightStore = writable<number>(500);
diff --git a/packages/svelte/src/lib/store/utils.ts b/packages/svelte/src/lib/store/utils.ts
index e924d832..0fa76828 100644
--- a/packages/svelte/src/lib/store/utils.ts
+++ b/packages/svelte/src/lib/store/utils.ts
@@ -18,7 +18,8 @@ import {
   type NodeOrigin,
   infiniteExtent,
   type CoordinateExtent,
-  fitViewport
+  fitViewport,
+  withResolvers
 } from '@xyflow/system';
 
 import type {
@@ -145,7 +146,7 @@ export const createNodesStore = (
   nodeExtent: CoordinateExtent = infiniteExtent,
   fitViewQueued: Writable<boolean>,
   fitViewOptions: Writable<FitViewOptions | undefined>,
-  fitViewResolver: Writable<PromiseWithResolvers<boolean> | null>,
+  fitViewResolver: Writable<ReturnType<typeof withResolvers<boolean>> | null>,
   panZoom: Writable<PanZoomInstance | null>,
   width: Writable<number>,
   height: Writable<number>,
diff --git a/packages/system/src/utils/general.ts b/packages/system/src/utils/general.ts
index 67743b5d..0e9b8d85 100644
--- a/packages/system/src/utils/general.ts
+++ b/packages/system/src/utils/general.ts
@@ -399,3 +399,22 @@ export function areSetsEqual(a: Set<string>, b: Set<string>) {
 
   return true;
 }
+
+/**
+ * Polyfill for Promise.withResolvers until we can use it in all browsers
+ * @internal
+ */
+export function withResolvers<T>(): {
+  promise: Promise<T>;
+  resolve: (value: T | PromiseLike<T>) => void;
+  reject: (reason?: unknown) => void;
+} {
+  let resolve!: (value: T | PromiseLike<T>) => void;
+  let reject!: (reason?: unknown) => void;
+
+  const promise = new Promise<T>((res, rej) => {
+    resolve = res;
+    reject = rej;
+  });
+  return { promise, resolve, reject };
+}