diff --git a/src/impls.rs b/src/impls.rs
index c496618..4b6e6bd 100644
--- a/src/impls.rs
+++ b/src/impls.rs
@@ -1,5 +1,6 @@
 mod add;
 mod index;
 mod intersection;
-mod sub;
+mod sub_iterable;
+mod sub_self;
 mod union;
diff --git a/src/impls/sub_iterable.rs b/src/impls/sub_iterable.rs
new file mode 100644
index 0000000..15e5f81
--- /dev/null
+++ b/src/impls/sub_iterable.rs
@@ -0,0 +1,57 @@
+use crate::Counter;
+
+use num_traits::{One, Zero};
+
+use std::hash::Hash;
+use std::ops::{Sub, SubAssign};
+
+impl<I, T, N> Sub<I> for Counter<T, N>
+where
+    I: IntoIterator<Item = T>,
+    T: Hash + Eq,
+    N: PartialOrd + SubAssign + Zero + One,
+{
+    type Output = Self;
+    /// Consume `self` producing a `Counter` like `self` with the counts of the
+    /// elements of `I` subtracted, keeping only positive values.
+    ///
+    /// ```rust
+    /// # use counter::Counter;
+    /// # use std::collections::HashMap;
+    /// let c = "aaab".chars().collect::<Counter<_>>();
+    /// let e = c - "abb".chars();
+    ///
+    /// let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
+    /// assert_eq!(e.into_map(), expect);
+    /// ```
+    fn sub(mut self, rhs: I) -> Self::Output {
+        self.subtract(rhs);
+        self
+    }
+}
+
+impl<I, T, N> SubAssign<I> for Counter<T, N>
+where
+    I: IntoIterator<Item = T>,
+    T: Hash + Eq,
+    N: PartialOrd + SubAssign + Zero + One,
+{
+    /// Directly subtract the counts of the elements of `I` from `self`,
+    /// keeping only items with a value greater than [`N::zero()`].
+    ///
+    /// [`N::zero()`]:
+    /// https://docs.rs/num-traits/latest/num_traits/identities/trait.Zero.html#tymethod.zero
+    ///
+    /// ```rust
+    /// # use counter::Counter;
+    /// # use std::collections::HashMap;
+    /// let mut c = "aaab".chars().collect::<Counter<_>>();
+    /// c -= "abb".chars();
+    ///
+    /// let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
+    /// assert_eq!(c.into_map(), expect);
+    /// ```
+    fn sub_assign(&mut self, rhs: I) {
+        self.subtract(rhs);
+    }
+}
diff --git a/src/impls/sub.rs b/src/impls/sub_self.rs
similarity index 59%
rename from src/impls/sub.rs
rename to src/impls/sub_self.rs
index 9413dcf..a213527 100644
--- a/src/impls/sub.rs
+++ b/src/impls/sub_self.rs
@@ -1,6 +1,6 @@
 use crate::Counter;
 
-use num_traits::{One, Zero};
+use num_traits::Zero;
 
 use std::hash::Hash;
 use std::ops::{Sub, SubAssign};
@@ -80,54 +80,3 @@ where
         }
     }
 }
-
-impl<I, T, N> Sub<I> for Counter<T, N>
-where
-    I: IntoIterator<Item = T>,
-    T: Hash + Eq,
-    N: PartialOrd + SubAssign + Zero + One,
-{
-    type Output = Self;
-    /// Consume `self` producing a `Counter` like `self` with the counts of the
-    /// elements of `I` subtracted, keeping only positive values.
-    ///
-    /// ```rust
-    /// # use counter::Counter;
-    /// # use std::collections::HashMap;
-    /// let c = "aaab".chars().collect::<Counter<_>>();
-    /// let e = c - "abb".chars();
-    ///
-    /// let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
-    /// assert_eq!(e.into_map(), expect);
-    /// ```
-    fn sub(mut self, rhs: I) -> Self::Output {
-        self.subtract(rhs);
-        self
-    }
-}
-
-impl<I, T, N> SubAssign<I> for Counter<T, N>
-where
-    I: IntoIterator<Item = T>,
-    T: Hash + Eq,
-    N: PartialOrd + SubAssign + Zero + One,
-{
-    /// Directly subtract the counts of the elements of `I` from `self`,
-    /// keeping only items with a value greater than [`N::zero()`].
-    ///
-    /// [`N::zero()`]:
-    /// https://docs.rs/num-traits/latest/num_traits/identities/trait.Zero.html#tymethod.zero
-    ///
-    /// ```rust
-    /// # use counter::Counter;
-    /// # use std::collections::HashMap;
-    /// let mut c = "aaab".chars().collect::<Counter<_>>();
-    /// c -= "abb".chars();
-    ///
-    /// let expect = [('a', 2)].iter().cloned().collect::<HashMap<_, _>>();
-    /// assert_eq!(c.into_map(), expect);
-    /// ```
-    fn sub_assign(&mut self, rhs: I) {
-        self.subtract(rhs);
-    }
-}