diff --git a/packages/react-aria/src/listbox/useOption.ts b/packages/react-aria/src/listbox/useOption.ts
index dbab6edf899..0a89c1ef2c8 100644
--- a/packages/react-aria/src/listbox/useOption.ts
+++ b/packages/react-aria/src/listbox/useOption.ts
@@ -16,6 +16,7 @@ import {DOMAttributes, FocusableElement, Key, RefObject} from '@react-types/shar
 import {filterDOMProps} from '../utils/filterDOMProps';
 import {getItemCount} from 'react-stately/private/collections/getItemCount';
 import {getItemId, listData} from './utils';
+import {getPosInSet} from '../utils/posinset';
 import {isFocusVisible} from '../interactions/useFocusVisible';
 import {ListState} from 'react-stately/useListState';
 import {mergeProps} from '../utils/mergeProps';
@@ -128,8 +129,8 @@ export function useOption<T>(
 
   let item = state.collection.getItem(key);
   if (isVirtualized) {
-    let index = Number(item?.index);
-    optionProps['aria-posinset'] = Number.isNaN(index) ? undefined : index + 1;
+    let posInSet = getPosInSet(state.collection, key, item);
+    optionProps['aria-posinset'] = Number.isNaN(posInSet) ? undefined : posInSet;
     optionProps['aria-setsize'] = getItemCount(state.collection);
   }
 
diff --git a/packages/react-aria/src/menu/useMenuItem.ts b/packages/react-aria/src/menu/useMenuItem.ts
index d38d3958e5a..7f301ced23d 100644
--- a/packages/react-aria/src/menu/useMenuItem.ts
+++ b/packages/react-aria/src/menu/useMenuItem.ts
@@ -25,6 +25,7 @@ import {
 import {filterDOMProps} from '../utils/filterDOMProps';
 import {getEventTarget} from '../utils/shadowdom/DOMFunctions';
 import {getItemCount} from 'react-stately/private/collections/getItemCount';
+import {getPosInSet} from '../utils/posinset';
 import {handleLinkClick, useLinkProps, useRouter} from '../utils/openLink';
 import {isFocusVisible, setInteractionModality} from '../interactions/useFocusVisible';
 import {menuData} from './utils';
@@ -225,8 +226,8 @@ export function useMenuItem<T>(
   }
 
   if (isVirtualized) {
-    let index = Number(item?.index);
-    ariaProps['aria-posinset'] = Number.isNaN(index) ? undefined : index + 1;
+    let posInSet = getPosInSet(state.collection, key, item);
+    ariaProps['aria-posinset'] = Number.isNaN(posInSet) ? undefined : posInSet;
     ariaProps['aria-setsize'] = getItemCount(state.collection);
   }
 
diff --git a/packages/react-aria/src/utils/posinset.ts b/packages/react-aria/src/utils/posinset.ts
new file mode 100644
index 00000000000..507f0e96c2e
--- /dev/null
+++ b/packages/react-aria/src/utils/posinset.ts
@@ -0,0 +1,54 @@
+/*
+ * Copyright 2020 Adobe. All rights reserved.
+ * This file is licensed to you under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License. You may obtain a copy
+ * of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under
+ * the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR REPRESENTATIONS
+ * OF ANY KIND, either express or implied. See the License for the specific language
+ * governing permissions and limitations under the License.
+ */
+
+import {Collection, Key, Node} from '@react-types/shared';
+import {getChildNodes} from 'react-stately/private/collections/getChildNodes';
+
+/**
+ * Computes the 1-based position of an item within the whole set of items, ignoring
+ * section headers. `item.index` restarts at 0 within each section, but `aria-setsize`
+ * is the global item count (see getItemCount), so the position must be global too -
+ * otherwise aria-posinset/aria-setsize are inconsistent for sectioned collections.
+ * Items that are not inside a section keep their existing O(1) index-based position.
+ */
+export function getPosInSet<T>(
+  collection: Collection<Node<T>>,
+  key: Key,
+  item: Node<T> | null
+): number {
+  if (item == null) {
+    return NaN;
+  }
+
+  // Not inside a section: the flat index is already correct.
+  if (item.parentKey == null) {
+    return Number(item.index) + 1;
+  }
+
+  // Inside a section: add the item count of every preceding section, then the
+  // item's position within its own section.
+  let position = Number(item.index) + 1;
+  for (let node of collection) {
+    if (node.key === item.parentKey) {
+      break;
+    }
+    if (node.type === 'section') {
+      for (let child of getChildNodes(node, collection)) {
+        if (child.type === 'item') {
+          position++;
+        }
+      }
+    }
+  }
+
+  return position;
+}
diff --git a/packages/react-aria/test/menu/useMenu.test.tsx b/packages/react-aria/test/menu/useMenu.test.tsx
index 9b19bbec8dc..f1abdc5300f 100644
--- a/packages/react-aria/test/menu/useMenu.test.tsx
+++ b/packages/react-aria/test/menu/useMenu.test.tsx
@@ -13,6 +13,8 @@
 import {AriaMenuProps, useMenu} from '../../src/menu/useMenu';
 
 import {Item} from 'react-stately/Item';
+import {Section} from 'react-stately/Section';
+import {getChildNodes} from 'react-stately/private/collections/getChildNodes';
 import {Key} from '@react-types/shared';
 import {pointerMap, render} from '@react-spectrum/test-utils-internal';
 import React from 'react';
@@ -81,6 +83,33 @@ function VirtualizedMenu<T extends object>(props: AriaMenuProps<T>) {
   );
 }
 
+function VirtualizedMenuWithSections<T extends object>(props: AriaMenuProps<T>) {
+  let state = useTreeState(props);
+  let ref = React.useRef(null);
+  let {menuProps} = useMenu(props, state, ref);
+
+  // Flatten sections into their items so useMenuItem is invoked for each item,
+  // mirroring how the real listbox iterates a sectioned collection.
+  let nodes: {key: Key; rendered: React.ReactNode; index?: number}[] = [];
+  for (let node of state.collection) {
+    if (node.type === 'section') {
+      for (let child of getChildNodes(node, state.collection)) {
+        nodes.push(child);
+      }
+    } else if (node.type === 'item') {
+      nodes.push(node);
+    }
+  }
+
+  return (
+    <ul {...menuProps} ref={ref}>
+      {nodes.map(item => (
+        <VirtualizedMenuItem key={item.key} item={item} state={state} />
+      ))}
+    </ul>
+  );
+}
+
 describe('useMenuTrigger', function () {
   let user;
   beforeAll(() => {
@@ -137,4 +166,29 @@ describe('useMenuItem with isVirtualized', function () {
     expect(items[1]).toHaveAttribute('aria-setsize', '3');
     expect(items[2]).toHaveAttribute('aria-setsize', '3');
   });
+
+  it('sets global aria-posinset across sections', () => {
+    let {getAllByRole} = render(
+      <VirtualizedMenuWithSections aria-label="test menu">
+        <Section title="Group 1">
+          <Item key="1">One</Item>
+          <Item key="2">Two</Item>
+        </Section>
+        <Section title="Group 2">
+          <Item key="3">Three</Item>
+          <Item key="4">Four</Item>
+        </Section>
+      </VirtualizedMenuWithSections>
+    );
+
+    // aria-posinset should be global (1..4) and match aria-setsize, not restart
+    // per section (which would report 1..2 for both groups).
+    let items = getAllByRole('menuitem');
+    expect(items[0]).toHaveAttribute('aria-posinset', '1');
+    expect(items[1]).toHaveAttribute('aria-posinset', '2');
+    expect(items[2]).toHaveAttribute('aria-posinset', '3');
+    expect(items[3]).toHaveAttribute('aria-posinset', '4');
+    expect(items[0]).toHaveAttribute('aria-setsize', '4');
+    expect(items[3]).toHaveAttribute('aria-setsize', '4');
+  });
 });