diff --git a/src/func/instances/composition.rs b/src/func/instances/composition.rs
index 8e9440b..135ae21 100644
--- a/src/func/instances/composition.rs
+++ b/src/func/instances/composition.rs
@@ -187,22 +187,34 @@ mod composition_tests {
 
     type T = CompositionInstance<OptionInstance, ResultInstance<i32>>;
 
-    impl<'a> tests::ToEq<'a> for T {
-        type Eq<A: 'a + Send + PartialEq + std::fmt::Debug> = Self::F<A>;
+    impl<'a, U: tests::ToEq<'a> + Functor<'a>, V: tests::ToEq<'a>> tests::ToEq<'a>
+        for CompositionInstance<U, V>
+    {
+        type Eq<A: 'a + Send + PartialEq + std::fmt::Debug> = U::Eq<V::Eq<A>>;
 
         fn to_eq<A: 'a + Send + PartialEq + std::fmt::Debug>(fa: Self::F<A>) -> Self::Eq<A> {
-            fa
+            U::to_eq(U::fmap(fa, V::to_eq))
         }
     }
 
-    impl<'a> test_suite::FunctorTestSuite<'a> for T {
+    fn regularise<'a, U: WeakFunctor<'a>, V: WeakFunctor<'a>, A: 'a + Send>(
+        fua: U::F<V::F<A>>,
+    ) -> <CompositionInstance<U, V> as WeakFunctor<'a>>::F<A> {
+        fua
+    }
+
+    impl<'a, U: test_suite::FunctorTestSuite<'a>, V: test_suite::FunctorTestSuite<'a>>
+        test_suite::FunctorTestSuite<'a> for CompositionInstance<U, V>
+    where
+        Self: tests::Eqr<'a>,
+    {
         fn sample<A: 'a + Send, F: FnMut(Arc<dyn test_suite::WrapFunction<'a, A, Self::F<A>>>)>(
             mut f: F,
         ) {
-            OptionInstance::sample(|ua0| {
-                ResultInstance::sample(|a0| {
+            U::sample(|ua0| {
+                V::sample(|a0| {
                     let ua0 = ua0.clone();
-                    f(Arc::new(move |a| ua0(a0(a))))
+                    f(Arc::new(move |a| regularise(ua0(a0(a)))))
                 })
             });
         }
diff --git a/src/func/tests.rs b/src/func/tests.rs
index 356f6ec..f971435 100644
--- a/src/func/tests.rs
+++ b/src/func/tests.rs
@@ -41,7 +41,7 @@ pub trait Eqr<'a>: WeakFunctor<'a> {
 }
 
 pub trait ToEq<'a>: WeakFunctor<'a> {
-    type Eq<A: 'a + Send + PartialEq + Debug>: PartialEq + Debug;
+    type Eq<A: 'a + Send + PartialEq + Debug>: 'a + Send + PartialEq + Debug;
 
     fn to_eq<A: 'a + Send + PartialEq + Debug>(fa: Self::F<A>) -> Self::Eq<A>;
 }