diff --git a/tests/object/crush.test-d.ts b/tests/object/crush.test-d.ts
new file mode 100644
index 00000000..059db22c
--- /dev/null
+++ b/tests/object/crush.test-d.ts
@@ -0,0 +1,53 @@
+import * as _ from 'radashi'
+
+describe('crush', () => {
+  test('direct properties are preserved in the result type', () => {
+    const obj = _.crush({ a: 1, b: '2', c: true })
+    expectTypeOf(obj).toEqualTypeOf<{ a: number; b: string; c: boolean }>()
+  })
+  test('nested objects add Record to result type', () => {
+    const obj = _.crush({ a: { b: 1 } })
+    expectTypeOf(obj).toEqualTypeOf<Record<string, unknown>>()
+
+    const obj2 = _.crush({ a: 1, b: { c: 2 } })
+    expectTypeOf(obj2).toEqualTypeOf<{ a: number; [key: string]: unknown }>()
+    expectTypeOf(obj2.a).toEqualTypeOf<number>()
+    expectTypeOf(obj2['b.c']).toEqualTypeOf<unknown>()
+  })
+  test('optional property', () => {
+    const obj = _.crush({} as { a?: number })
+    // FIXME: Try to preserve optionality.
+    expectTypeOf(obj).toEqualTypeOf<{ a: number | undefined }>()
+  })
+  test('crushed Record type', () => {
+    const obj = _.crush({} as Record<number, number>)
+    expectTypeOf(obj).toEqualTypeOf<Record<number, number>>()
+
+    const obj2 = _.crush({} as Record<string, string>)
+    expectTypeOf(obj2).toEqualTypeOf<Record<string, string>>()
+
+    const obj3 = _.crush({} as Record<number, number | object>)
+    expectTypeOf(obj3).toEqualTypeOf<Record<string, unknown>>()
+
+    const obj4 = _.crush({} as Record<string, string | unknown[]>)
+    expectTypeOf(obj4).toEqualTypeOf<Record<string, unknown>>()
+  })
+  test('crushed array', () => {
+    // We cannot assume the keys from "number[]" input value, but we
+    // *can* assume the value type. Note that the value type doesn't
+    // contain "undefined" (which matches array behavior).
+    const obj = _.crush([1, 2, 3])
+    expectTypeOf(obj).toEqualTypeOf<Record<string, number>>()
+
+    const obj2 = _.crush([1, { b: 2 }])
+    expectTypeOf(obj2).toEqualTypeOf<Record<string, unknown>>()
+    expectTypeOf(obj2[0]).toEqualTypeOf<unknown>()
+  })
+  test('union type with object and primitive', () => {
+    // Since "a" may be an object, we cannot assume the result will
+    // have an "a" property. Therefore, the keys and values of the
+    // result are unknown.
+    const obj = _.crush({ a: {} as number | object })
+    expectTypeOf(obj).toEqualTypeOf<Record<string, unknown>>()
+  })
+})
diff --git a/tests/object/crush.test.ts b/tests/object/crush.test.ts
index 16cfd0af..3645a8d6 100644
--- a/tests/object/crush.test.ts
+++ b/tests/object/crush.test.ts
@@ -33,30 +33,6 @@ describe('crush', () => {
       timestamp: now,
     })
   })
-  test('handles property names with dots 1', () => {
-    const obj = {
-      a: { 'b.c': 'value' },
-    }
-    expect(_.crush(obj)).toEqual({
-      'a.b.c': 'value',
-    })
-  })
-  test('handles property names with dots 2', () => {
-    const obj = {
-      'a.b': { c: 'value' },
-    }
-    expect(_.crush(obj)).toEqual({
-      'a.b.c': 'value',
-    })
-  })
-  test('handles property names with dots 3', () => {
-    const obj = {
-      'a.b': { 'c.d': 123.4 },
-    }
-    expect(_.crush(obj)).toEqual({
-      'a.b.c.d': 123.4,
-    })
-  })
   test('handles arrays', () => {
     const obj = ['value', 123.4, true]
     expect(_.crush(obj)).toEqual({
@@ -65,4 +41,59 @@ describe('crush', () => {
       '2': true,
     })
   })
+  describe('property names containing period', () => {
+    test('inside the root object', () => {
+      const obj = {
+        'a.b': { c: 'value' },
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b.c': 'value',
+      })
+    })
+    test('inside a nested object', () => {
+      const obj = {
+        a: { 'b.c': 'value' },
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b.c': 'value',
+      })
+    })
+    test('inside both root and nested object', () => {
+      const obj = {
+        'a.b': { 'c.d': 123.4 },
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b.c.d': 123.4,
+      })
+    })
+    test('crush array containing object with nested property', () => {
+      const arr = [{ 'c.d': { 'e.f': 'g' } }]
+      const obj = {
+        'a.b': arr,
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b.0.c.d.e.f': 'g',
+      })
+    })
+    test('do not crush Date objects', () => {
+      const date = new Date()
+      const obj = {
+        'a.b': date,
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b': date,
+      })
+    })
+    test('do not crush Map objects', () => {
+      const map = new Map()
+      map.set('a', 'b')
+      map.set('c', 'd')
+      const obj = {
+        'a.b': map,
+      }
+      expect(_.crush(obj)).toEqual({
+        'a.b': map,
+      })
+    })
+  })
 })