diff --git a/ChangeLog-8.0.md b/ChangeLog-8.0.md
index 1f9ebec4b35..07495abae5e 100644
--- a/ChangeLog-8.0.md
+++ b/ChangeLog-8.0.md
@@ -8,6 +8,7 @@ All notable changes of the PHPUnit 8.0 release series are documented in this fil
 
 * Implemented [#3288](https://github.com/sebastianbergmann/phpunit/issues/3288): The `void_return` fixer of php-cs-fixer is now in effect
 * Implemented [#3341](https://github.com/sebastianbergmann/phpunit/issues/3341): Deprecate optional parameters of `assertEquals()` and `assertNotEquals()`
+* Implemented [#3369](https://github.com/sebastianbergmann/phpunit/issues/3369): Deprecate `assertInternalType()` and `assertNotInternalType()`
 
 ### Removed
 
diff --git a/src/Framework/Assert.php b/src/Framework/Assert.php
index 3c80c1a54fb..1f460e3497f 100644
--- a/src/Framework/Assert.php
+++ b/src/Framework/Assert.php
@@ -1581,6 +1581,8 @@ public static function assertAttributeNotInstanceOf(string $expected, string $at
      */
     public static function assertInternalType(string $expected, $actual, string $message = ''): void
     {
+        self::createWarning('assertInternalType() is deprecated and will be removed in PHPUnit 9. Refactor your test to use assertIsArray(), assertIsBool(), assertIsFloat(), assertIsInt(), assertIsNumeric(), assertIsObject(), assertIsResource(), assertIsString(), assertIsScalar(), assertIsCallable(), or assertIsIterable() instead.');
+
         static::assertThat(
             $actual,
             new IsType($expected),
@@ -1749,6 +1751,8 @@ public static function assertIsIterable($actual, string $message = ''): void
      */
     public static function assertNotInternalType(string $expected, $actual, string $message = ''): void
     {
+        self::createWarning('assertNotInternalType() is deprecated and will be removed in PHPUnit 9. Refactor your test to use assertIsNotArray(), assertIsNotBool(), assertIsNotFloat(), assertIsNotInt(), assertIsNotNumeric(), assertIsNotObject(), assertIsNotResource(), assertIsNotString(), assertIsNotScalar(), assertIsNotCallable(), or assertIsNotIterable() instead.');
+
         static::assertThat(
             $actual,
             new LogicalNot(
diff --git a/tests/unit/Framework/AssertTest.php b/tests/unit/Framework/AssertTest.php
index f717d64f142..b71bec3ab76 100644
--- a/tests/unit/Framework/AssertTest.php
+++ b/tests/unit/Framework/AssertTest.php
@@ -2431,24 +2431,6 @@ public function testAssertAttributeNotInstanceOf(): void
         $this->assertAttributeNotInstanceOf(\Exception::class, 'a', $o);
     }
 
-    public function testAssertInternalType(): void
-    {
-        $this->assertInternalType('integer', 1);
-
-        $this->expectException(AssertionFailedError::class);
-
-        $this->assertInternalType('string', 1);
-    }
-
-    public function testAssertInternalTypeDouble(): void
-    {
-        $this->assertInternalType('double', 1.0);
-
-        $this->expectException(AssertionFailedError::class);
-
-        $this->assertInternalType('double', 1);
-    }
-
     public function testAssertAttributeInternalType(): void
     {
         $o    = new \stdClass;
@@ -2457,15 +2439,6 @@ public function testAssertAttributeInternalType(): void
         $this->assertAttributeInternalType('integer', 'a', $o);
     }
 
-    public function testAssertNotInternalType(): void
-    {
-        $this->assertNotInternalType('string', 1);
-
-        $this->expectException(AssertionFailedError::class);
-
-        $this->assertNotInternalType('integer', 1);
-    }
-
     public function testAssertAttributeNotInternalType(): void
     {
         $o    = new \stdClass;