From b183743e0e4cfe574ed404836b2c97e1e8df6c44 Mon Sep 17 00:00:00 2001
From: alex-js-ltd <alex.js.ltd@gmail.com>
Date: Tue, 24 Mar 2026 14:39:10 +0000
Subject: [PATCH 1/3] fix: use Object.is instead of === in replaceEqualDeep for
 NaN equality

---
 packages/query-core/src/__tests__/utils.test.tsx | 6 ++++++
 packages/query-core/src/utils.ts                 | 4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/packages/query-core/src/__tests__/utils.test.tsx b/packages/query-core/src/__tests__/utils.test.tsx
index 9cee1b46424..7b051b90f8e 100644
--- a/packages/query-core/src/__tests__/utils.test.tsx
+++ b/packages/query-core/src/__tests__/utils.test.tsx
@@ -416,6 +416,12 @@ describe('core/utils', () => {
 
       expect(next).toBe(current)
     })
+
+    it('should return the previous object reference when values contain NaN', () => {
+      const prev = { value: NaN }
+      const next = { value: NaN }
+      expect(replaceEqualDeep(prev, next)).toBe(prev)
+    })
   })
 
   describe('matchMutation', () => {
diff --git a/packages/query-core/src/utils.ts b/packages/query-core/src/utils.ts
index b29e8ded456..109d02d11f1 100644
--- a/packages/query-core/src/utils.ts
+++ b/packages/query-core/src/utils.ts
@@ -269,7 +269,7 @@ const hasOwn = Object.prototype.hasOwnProperty
  */
 export function replaceEqualDeep<T>(a: unknown, b: T, depth?: number): T
 export function replaceEqualDeep(a: any, b: any, depth = 0): any {
-  if (a === b) {
+  if (Object.is(a, b)) {
     return a
   }
 
@@ -292,7 +292,7 @@ export function replaceEqualDeep(a: any, b: any, depth = 0): any {
     const aItem = a[key]
     const bItem = b[key]
 
-    if (aItem === bItem) {
+    if (Object.is(aItem, bItem)) {
       copy[key] = aItem
       if (array ? i < aSize : hasOwn.call(a, key)) equalItems++
       continue

From 9a33a6872c6ceafe8303a7b818fde9a116886321 Mon Sep 17 00:00:00 2001
From: alex-js-ltd <alex.js.ltd@gmail.com>
Date: Tue, 24 Mar 2026 14:44:12 +0000
Subject: [PATCH 2/3] chore: add changeset

---
 .changeset/happy-banks-repeat.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/happy-banks-repeat.md

diff --git a/.changeset/happy-banks-repeat.md b/.changeset/happy-banks-repeat.md
new file mode 100644
index 00000000000..18d0e1f53bc
--- /dev/null
+++ b/.changeset/happy-banks-repeat.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+fix: use Object.is instead of === in replaceEqualDeep to correctly handle NaN equality

From d5fb45be1fc7cdde68efdb032d0f439012dd714c Mon Sep 17 00:00:00 2001
From: alex-js-ltd <alex.js.ltd@gmail.com>
Date: Tue, 24 Mar 2026 15:14:56 +0000
Subject: [PATCH 3/3] test: add NaN structural sharing test cases for
 replaceEqualDeep

---
 packages/query-core/src/__tests__/utils.test.tsx | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/packages/query-core/src/__tests__/utils.test.tsx b/packages/query-core/src/__tests__/utils.test.tsx
index 7b051b90f8e..f70069a3631 100644
--- a/packages/query-core/src/__tests__/utils.test.tsx
+++ b/packages/query-core/src/__tests__/utils.test.tsx
@@ -417,11 +417,21 @@ describe('core/utils', () => {
       expect(next).toBe(current)
     })
 
-    it('should return the previous object reference when values contain NaN', () => {
+    it('preserves reference when objects contain NaN', () => {
       const prev = { value: NaN }
       const next = { value: NaN }
       expect(replaceEqualDeep(prev, next)).toBe(prev)
     })
+
+    it('handles top-level NaN equality', () => {
+      expect(Number.isNaN(replaceEqualDeep(NaN, NaN))).toBe(true)
+    })
+
+    it('preserves reference for arrays containing NaN', () => {
+      const prev = [NaN, { a: 1 }]
+      const next = [NaN, { a: 1 }]
+      expect(replaceEqualDeep(prev, next)).toBe(prev)
+    })
   })
 
   describe('matchMutation', () => {