diff --git a/palette/src/serde/alpha_serializer.rs b/palette/src/serde/alpha_serializer.rs
index 094dd02d1..b1edd4a1e 100644
--- a/palette/src/serde/alpha_serializer.rs
+++ b/palette/src/serde/alpha_serializer.rs
@@ -79,13 +79,13 @@ where
         })
     }
 
-    fn serialize_newtype_struct<T: ?Sized>(
+    fn serialize_newtype_struct<T>(
         self,
         name: &'static str,
         value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: serde::Serialize,
+        T: serde::Serialize + ?Sized,
     {
         let mut serializer = self.serialize_tuple_struct(name, 1)?;
         serializer.serialize_field(value)?;
@@ -162,9 +162,9 @@ where
         alpha_serializer_error()
     }
 
-    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<Self::Ok, Self::Error>
+    fn serialize_some<T>(self, _value: &T) -> Result<Self::Ok, Self::Error>
     where
-        T: serde::Serialize,
+        T: serde::Serialize + ?Sized,
     {
         alpha_serializer_error()
     }
@@ -198,7 +198,7 @@ where
         alpha_serializer_error()
     }
 
-    fn serialize_newtype_variant<T: ?Sized>(
+    fn serialize_newtype_variant<T>(
         self,
         _name: &'static str,
         _variant_index: u32,
@@ -206,7 +206,7 @@ where
         _value: &T,
     ) -> Result<Self::Ok, Self::Error>
     where
-        T: serde::Serialize,
+        T: serde::Serialize + ?Sized,
     {
         alpha_serializer_error()
     }
@@ -239,9 +239,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_element(value)
     }
@@ -261,9 +261,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_element<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_element(value)
     }
@@ -283,9 +283,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_field(value)
     }
@@ -305,9 +305,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_field(value)
     }
@@ -327,28 +327,24 @@ where
 
     type Error = S::Error;
 
-    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), Self::Error>
+    fn serialize_key<T>(&mut self, key: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_key(key)
     }
 
-    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+    fn serialize_value<T>(&mut self, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_value(value)
     }
 
-    fn serialize_entry<K: ?Sized, V: ?Sized>(
-        &mut self,
-        key: &K,
-        value: &V,
-    ) -> Result<(), Self::Error>
+    fn serialize_entry<K, V>(&mut self, key: &K, value: &V) -> Result<(), Self::Error>
     where
-        K: Serialize,
-        V: Serialize,
+        K: Serialize + ?Sized,
+        V: Serialize + ?Sized,
     {
         self.inner.serialize_entry(key, value)
     }
@@ -368,13 +364,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_field(key, value)
     }
@@ -398,13 +390,9 @@ where
 
     type Error = S::Error;
 
-    fn serialize_field<T: ?Sized>(
-        &mut self,
-        key: &'static str,
-        value: &T,
-    ) -> Result<(), Self::Error>
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<(), Self::Error>
     where
-        T: Serialize,
+        T: Serialize + ?Sized,
     {
         self.inner.serialize_field(key, value)
     }