diff --git a/.changeset/fix-shallow-mismatched-types-and-invalid-dates.md b/.changeset/fix-shallow-mismatched-types-and-invalid-dates.md
new file mode 100644
index 00000000..55606090
--- /dev/null
+++ b/.changeset/fix-shallow-mismatched-types-and-invalid-dates.md
@@ -0,0 +1,5 @@
+---
+"@tanstack/store": patch
+---
+
+fix(store): guard `shallow` comparison against mismatched collection types and support invalid dates
diff --git a/packages/store/src/shallow.ts b/packages/store/src/shallow.ts
index 75ff1634..54f575c6 100644
--- a/packages/store/src/shallow.ts
+++ b/packages/store/src/shallow.ts
@@ -12,7 +12,8 @@ export function shallow<T>(objA: T, objB: T) {
     return false
   }
 
-  if (objA instanceof Map && objB instanceof Map) {
+  if (objA instanceof Map || objB instanceof Map) {
+    if (!(objA instanceof Map) || !(objB instanceof Map)) return false
     if (objA.size !== objB.size) return false
     for (const [k, v] of objA) {
       if (!objB.has(k) || !Object.is(v, objB.get(k))) return false
@@ -20,7 +21,8 @@ export function shallow<T>(objA: T, objB: T) {
     return true
   }
 
-  if (objA instanceof Set && objB instanceof Set) {
+  if (objA instanceof Set || objB instanceof Set) {
+    if (!(objA instanceof Set) || !(objB instanceof Set)) return false
     if (objA.size !== objB.size) return false
     for (const v of objA) {
       if (!objB.has(v)) return false
@@ -28,9 +30,9 @@ export function shallow<T>(objA: T, objB: T) {
     return true
   }
 
-  if (objA instanceof Date && objB instanceof Date) {
-    if (objA.getTime() !== objB.getTime()) return false
-    return true
+  if (objA instanceof Date || objB instanceof Date) {
+    if (!(objA instanceof Date) || !(objB instanceof Date)) return false
+    return Object.is(objA.getTime(), objB.getTime())
   }
 
   const keysA = getOwnKeys(objA)
diff --git a/packages/store/tests/shallow.test.ts b/packages/store/tests/shallow.test.ts
new file mode 100644
index 00000000..e5b4f77f
--- /dev/null
+++ b/packages/store/tests/shallow.test.ts
@@ -0,0 +1,84 @@
+import { describe, expect, test } from 'vitest'
+import { shallow } from '../src/shallow'
+
+describe('shallow', () => {
+  test('returns true for identical primitives and references', () => {
+    expect(shallow(1, 1)).toBe(true)
+    expect(shallow('a', 'a')).toBe(true)
+    expect(shallow(true, true)).toBe(true)
+    expect(shallow(null, null)).toBe(true)
+    expect(shallow(undefined, undefined)).toBe(true)
+    expect(shallow(NaN, NaN)).toBe(true)
+
+    const obj = { a: 1 }
+    expect(shallow(obj, obj)).toBe(true)
+  })
+
+  test('returns false for different primitives or nullish mismatches', () => {
+    expect(shallow(1, 2)).toBe(false)
+    expect(shallow('a', 'b')).toBe(false)
+    expect(shallow(true, false)).toBe(false)
+    expect(shallow(null, undefined)).toBe(false)
+    expect(shallow({}, null)).toBe(false)
+    expect(shallow(null, {})).toBe(false)
+  })
+
+  test('compares plain objects by shallow keys and values', () => {
+    expect(shallow({ a: 1, b: 'x' }, { a: 1, b: 'x' })).toBe(true)
+    expect(shallow({ a: 1, b: 'x' }, { a: 1, b: 'y' })).toBe(false)
+    expect(shallow({ a: 1 }, { a: 1, b: 2 })).toBe(false)
+  })
+
+  test('compares arrays by element shallow equality', () => {
+    expect(shallow([1, 2, 3], [1, 2, 3])).toBe(true)
+    expect(shallow([1, 2], [1, 2, 3])).toBe(false)
+    expect(shallow([1, 'a'], [1, 'b'])).toBe(false)
+  })
+
+  test('compares Dates correctly, including invalid dates and mismatched types', () => {
+    const d1 = new Date(1700000000000)
+    const d2 = new Date(1700000000000)
+    const d3 = new Date(1700000000001)
+
+    expect(shallow(d1, d2)).toBe(true)
+    expect(shallow(d1, d3)).toBe(false)
+
+    const invalid1 = new Date('invalid')
+    const invalid2 = new Date('invalid')
+    expect(shallow(invalid1, invalid2)).toBe(true)
+    expect(shallow(d1, invalid1)).toBe(false)
+
+    expect(shallow(d1, {} as unknown as Date)).toBe(false)
+    expect(shallow({} as unknown as Date, d1)).toBe(false)
+  })
+
+  test('compares Maps correctly and rejects mismatched types', () => {
+    const m1 = new Map([['a', 1], ['b', 2]])
+    const m2 = new Map([['a', 1], ['b', 2]])
+    const m3 = new Map([['a', 1], ['b', 3]])
+
+    expect(shallow(m1, m2)).toBe(true)
+    expect(shallow(m1, m3)).toBe(false)
+
+    expect(shallow(m1, {} as unknown as Map<string, number>)).toBe(false)
+    expect(shallow({} as unknown as Map<string, number>, m1)).toBe(false)
+  })
+
+  test('compares Sets correctly and rejects mismatched types', () => {
+    const s1 = new Set([1, 2, 3])
+    const s2 = new Set([1, 2, 3])
+    const s3 = new Set([1, 2, 4])
+
+    expect(shallow(s1, s2)).toBe(true)
+    expect(shallow(s1, s3)).toBe(false)
+
+    expect(shallow(s1, {} as unknown as Set<number>)).toBe(false)
+    expect(shallow({} as unknown as Set<number>, s1)).toBe(false)
+  })
+
+  test('returns false when comparing distinct collection types against each other', () => {
+    expect(shallow(new Date(), new Map() as unknown as Date)).toBe(false)
+    expect(shallow(new Map(), new Set() as unknown as Map<unknown, unknown>)).toBe(false)
+    expect(shallow(new Set(), new Date() as unknown as Set<unknown>)).toBe(false)
+  })
+})