diff --git a/src/zipcartesian.rs b/src/zipcartesian.rs
index 77ce92b..0aae18b 100644
--- a/src/zipcartesian.rs
+++ b/src/zipcartesian.rs
@@ -1,24 +1,34 @@
 use std::iter::Iterator;
 
-pub trait ZipCartesianExt: Iterator {
+pub trait ZipCartesianExt: Iterator + Clone
+where
+    Self::Item: Copy,
+{
     fn zip_cartesian<B>(
         self,
         b: B,
     ) -> impl Iterator<Item = (Self::Item, B::Item)> + Clone
     where
-        Self::Item: Copy,
-        Self: Sized + Clone,
-        B: Iterator<Item: Copy> + Clone;
+        B::Item: Copy,
+        B: Iterator + Clone;
 }
 
-impl<I: Iterator<Item: Copy> + Clone> ZipCartesianExt for I {
+impl<I> ZipCartesianExt for I
+where
+    I: Iterator + Clone,
+    I::Item: Copy,
+{
     /// Exhaustive coupling of two iterators.
     /// For each x in `self`: for each y in `b`: yield (x, y).
     /// b: B must implement `Clone`.
-    fn zip_cartesian<B: Iterator<Item: Copy> + Clone>(
+    fn zip_cartesian<B>(
         self,
         b: B,
-    ) -> impl Iterator<Item = (Self::Item, B::Item)> + Clone {
+    ) -> impl Iterator<Item = (Self::Item, B::Item)> + Clone
+    where
+        B::Item: Copy,
+        B: Iterator + Clone,
+    {
         self.flat_map(move |a_item| {
             b.clone().map(move |b_item| (a_item, b_item))
         })