diff --git a/src/Type/PHPUnit/Assert/AssertTypeSpecifyingExtensionHelper.php b/src/Type/PHPUnit/Assert/AssertTypeSpecifyingExtensionHelper.php
index 2276b51..2e8e828 100644
--- a/src/Type/PHPUnit/Assert/AssertTypeSpecifyingExtensionHelper.php
+++ b/src/Type/PHPUnit/Assert/AssertTypeSpecifyingExtensionHelper.php
@@ -123,16 +123,10 @@ private static function getExpressionResolvers(): array
 	{
 		if (self::$resolvers === null) {
 			self::$resolvers = [
-				'InstanceOf' => static function (Scope $scope, Arg $class, Arg $object): ?Instanceof_ {
-					$classType = $scope->getType($class->value);
-					$classNames = $classType->getConstantStrings();
-					if (count($classNames) !== 1) {
-						return null;
-					}
-
+				'InstanceOf' => static function (Scope $scope, Arg $class, Arg $object): Instanceof_ {
 					return new Instanceof_(
 						$object->value,
-						new Name($classNames[0]->getValue())
+						$class->value
 					);
 				},
 				'Same' => static function (Scope $scope, Arg $expected, Arg $actual): Identical {
diff --git a/tests/Type/PHPUnit/data/assert-function.php b/tests/Type/PHPUnit/data/assert-function.php
index 117179a..f3222f3 100644
--- a/tests/Type/PHPUnit/data/assert-function.php
+++ b/tests/Type/PHPUnit/data/assert-function.php
@@ -20,6 +20,17 @@ public function doFoo($o): void
 		assertType(self::class, $o);
 	}
 
+	/**
+	 * @template T of object
+	 * @param object $o
+	 * @param class-string<\DateTimeInterface> $class
+	 */
+	public function assertInstanceOfWorksWithTemplate($o, $class): void
+	{
+		assertInstanceOf($class, $o);
+		assertType(\DateTimeInterface::class, $o);
+	}
+
 	public function arrayHasNumericKey(array $a): void {
 		assertArrayHasKey(0, $a);
 		assertType('array&hasOffset(0)', $a);