diff --git a/src/Constraint/IsType.hack b/src/Constraint/IsType.hack
index df4f2a8..b62d8d8 100644
--- a/src/Constraint/IsType.hack
+++ b/src/Constraint/IsType.hack
@@ -11,7 +11,7 @@ namespace Facebook\FBExpect\Constraint;
 
 use function Facebook\FBExpect\is_iterable;
 
-class IsType {
+final class IsType {
   const type TPredicate = (function(mixed): bool);
   public function __construct(private string $expectedType) {}
 
diff --git a/src/Constraint/TraversableContains.hack b/src/Constraint/TraversableContains.hack
index 12c1c6f..1dfbf8c 100644
--- a/src/Constraint/TraversableContains.hack
+++ b/src/Constraint/TraversableContains.hack
@@ -9,7 +9,7 @@
 
 namespace Facebook\FBExpect\Constraint;
 
-class TraversableContains {
+final class TraversableContains {
 
   public function __construct(private mixed $value) {}
 
diff --git a/src/ExpectObj.hack b/src/ExpectObj.hack
index 14ff328..d53118a 100644
--- a/src/ExpectObj.hack
+++ b/src/ExpectObj.hack
@@ -14,7 +14,7 @@ use namespace HH\Lib\{C, Str, Vec};
 use type HH\Lib\Ref;
 use type Facebook\HackTest\ExpectationFailedException;
 
-class ExpectObj<T> extends Assert {
+final class ExpectObj<T> extends Assert {
   public function __construct(private T $var) {}
 
   /**************************************
diff --git a/tests/ExpectObjTest.hack b/tests/ExpectObjTest.hack
index 65e17e6..9fbc87f 100644
--- a/tests/ExpectObjTest.hack
+++ b/tests/ExpectObjTest.hack
@@ -100,7 +100,7 @@ final class ExpectObjTest extends HackTest {
     expect('haystack')->toNotMatchRegExp('/needle/');
 
     // sorting
-    expect(vec[1, 2, 3])->toBeSortedBy(function(int $prev, int $curr): bool {
+    expect(vec[1, 2, 3])->toBeSortedBy((int $prev, int $curr): bool ==> {
       if ($prev <= $curr) {
         return true;
       }
@@ -218,7 +218,6 @@ final class ExpectObjTest extends HackTest {
     } else {
       expect(() ==> $rm->invokeArgs($obj, vec[$expected, 'custom msg']))
         ->toThrow(ExpectationFailedException::class, 'custom msg');
-      ;
     }
 
     // And with funky sprintfification
@@ -248,7 +247,7 @@ final class ExpectObjTest extends HackTest {
   //
   public function testToThrowWithMessage(): void {
     expect(
-      function() {
+      () ==> {
         expect(
           () ==> {
             throw new ExpectObjTestException('test 2');