diff --git a/src/either_or_both/mod.rs b/src/either_or_both/mod.rs
index 1122f37..4c5e051 100644
--- a/src/either_or_both/mod.rs
+++ b/src/either_or_both/mod.rs
@@ -1841,7 +1841,10 @@ impl<L, R> EitherOrBoth<L, R> {
     /// assert_eq!(value.map_right(map_right), EitherOrBoth::Left(1));
     /// ```
     #[inline]
-    pub fn map_right<T>(self, f: fn(R) -> T) -> EitherOrBoth<L, T> {
+    pub fn map_right<F, T>(self, f: F) -> EitherOrBoth<L, T>
+    where
+        F: FnOnce(R) -> T,
+    {
         map_each!(self; l, r => l, f(r))
     }