diff --git a/src/blocking_retry.rs b/src/blocking_retry.rs
index 9f5038f..6141889 100644
--- a/src/blocking_retry.rs
+++ b/src/blocking_retry.rs
@@ -58,13 +58,19 @@ where
 }
 
 /// Retry struct generated by [`Retryable`].
-pub struct BlockingRetry<B: Backoff, T, E, F: FnMut() -> Result<T, E>> {
+pub struct BlockingRetry<
+    B: Backoff,
+    T,
+    E,
+    F: FnMut() -> Result<T, E>,
+    RF = fn(&E) -> bool,
+    NF = fn(&E, Duration),
+> {
     backoff: B,
-    retryable: fn(&E) -> bool,
-    notify: fn(&E, Duration),
+    retryable: RF,
+    notify: NF,
     f: F,
 }
-
 impl<B, T, E, F> BlockingRetry<B, T, E, F>
 where
     B: Backoff,
@@ -79,7 +85,15 @@ where
             f,
         }
     }
+}
 
+impl<B, T, E, F, RF, NF> BlockingRetry<B, T, E, F, RF, NF>
+where
+    B: Backoff,
+    F: FnMut() -> Result<T, E>,
+    RF: FnMut(&E) -> bool,
+    NF: FnMut(&E, Duration),
+{
     /// Set the conditions for retrying.
     ///
     /// If not specified, we treat all errors as retryable.
@@ -105,9 +119,13 @@ where
     ///     Ok(())
     /// }
     /// ```
-    pub fn when(mut self, retryable: fn(&E) -> bool) -> Self {
-        self.retryable = retryable;
-        self
+    pub fn when<RN: FnMut(&E) -> bool>(self, retryable: RN) -> BlockingRetry<B, T, E, F, RN, NF> {
+        BlockingRetry {
+            backoff: self.backoff,
+            retryable,
+            notify: self.notify,
+            f: self.f,
+        }
     }
 
     /// Set to notify for everything retrying.
@@ -140,9 +158,13 @@ where
     ///     Ok(())
     /// }
     /// ```
-    pub fn notify(mut self, notify: fn(&E, Duration)) -> Self {
-        self.notify = notify;
-        self
+    pub fn notify<NN: FnMut(&E, Duration)>(self, notify: NN) -> BlockingRetry<B, T, E, F, RF, NN> {
+        BlockingRetry {
+            backoff: self.backoff,
+            retryable: self.retryable,
+            notify,
+            f: self.f,
+        }
     }
 
     /// Call the retried function.
@@ -245,4 +267,32 @@ mod tests {
         assert_eq!(*error_times.lock().unwrap(), 4);
         Ok(())
     }
+
+    #[test]
+    fn test_fn_mut_when_and_notify() -> anyhow::Result<()> {
+        let mut calls_retryable: Vec<()> = vec![];
+        let mut calls_notify: Vec<()> = vec![];
+
+        let f = || Err::<(), anyhow::Error>(anyhow::anyhow!("retryable"));
+
+        let backoff = ExponentialBuilder::default().with_min_delay(Duration::from_millis(1));
+        let result = f
+            .retry(&backoff)
+            .when(|_| {
+                calls_retryable.push(());
+                true
+            })
+            .notify(|_, _| {
+                calls_notify.push(());
+            })
+            .call();
+
+        assert!(result.is_err());
+        assert_eq!("retryable", result.unwrap_err().to_string());
+        // `f` always returns error "retryable", so it should be executed
+        // 4 times (retry 3 times).
+        assert_eq!(calls_retryable.len(), 4);
+        assert_eq!(calls_notify.len(), 3);
+        Ok(())
+    }
 }
diff --git a/src/retry.rs b/src/retry.rs
index c7e8734..232c7ba 100644
--- a/src/retry.rs
+++ b/src/retry.rs
@@ -85,10 +85,18 @@ where
 
 /// Retry struct generated by [`Retryable`].
 #[pin_project]
-pub struct Retry<B: Backoff, T, E, Fut: Future<Output = Result<T, E>>, FutureFn: FnMut() -> Fut> {
+pub struct Retry<
+    B: Backoff,
+    T,
+    E,
+    Fut: Future<Output = Result<T, E>>,
+    FutureFn: FnMut() -> Fut,
+    RF = fn(&E) -> bool,
+    NF = fn(&E, Duration),
+> {
     backoff: B,
-    retryable: fn(&E) -> bool,
-    notify: fn(&E, Duration),
+    retryable: RF,
+    notify: NF,
     future_fn: FutureFn,
 
     #[pin]
@@ -111,7 +119,16 @@ where
             state: State::Idle,
         }
     }
+}
 
+impl<B, T, E, Fut, FutureFn, RF, NF> Retry<B, T, E, Fut, FutureFn, RF, NF>
+where
+    B: Backoff,
+    Fut: Future<Output = Result<T, E>>,
+    FutureFn: FnMut() -> Fut,
+    RF: FnMut(&E) -> bool,
+    NF: FnMut(&E, Duration),
+{
     /// Set the conditions for retrying.
     ///
     /// If not specified, we treat all errors as retryable.
@@ -141,9 +158,17 @@ where
     ///     Ok(())
     /// }
     /// ```
-    pub fn when(mut self, retryable: fn(&E) -> bool) -> Self {
-        self.retryable = retryable;
-        self
+    pub fn when<RN: FnMut(&E) -> bool>(
+        self,
+        retryable: RN,
+    ) -> Retry<B, T, E, Fut, FutureFn, RN, NF> {
+        Retry {
+            backoff: self.backoff,
+            retryable,
+            notify: self.notify,
+            future_fn: self.future_fn,
+            state: self.state,
+        }
     }
 
     /// Set to notify for everything retrying.
@@ -179,9 +204,17 @@ where
     ///     Ok(())
     /// }
     /// ```
-    pub fn notify(mut self, notify: fn(&E, Duration)) -> Self {
-        self.notify = notify;
-        self
+    pub fn notify<NN: FnMut(&E, Duration)>(
+        self,
+        notify: NN,
+    ) -> Retry<B, T, E, Fut, FutureFn, RF, NN> {
+        Retry {
+            backoff: self.backoff,
+            retryable: self.retryable,
+            notify,
+            future_fn: self.future_fn,
+            state: self.state,
+        }
     }
 }
 
@@ -201,11 +234,13 @@ enum State<T, E, Fut: Future<Output = Result<T, E>>> {
     Sleeping(#[pin] Pin<Box<tokio::time::Sleep>>),
 }
 
-impl<B, T, E, Fut, FutureFn> Future for Retry<B, T, E, Fut, FutureFn>
+impl<B, T, E, Fut, FutureFn, RF, NF> Future for Retry<B, T, E, Fut, FutureFn, RF, NF>
 where
     B: Backoff,
     Fut: Future<Output = Result<T, E>>,
     FutureFn: FnMut() -> Fut,
+    RF: FnMut(&E) -> bool,
+    NF: FnMut(&E, Duration),
 {
     type Output = Result<T, E>;
 
@@ -320,4 +355,32 @@ mod tests {
         assert_eq!(*error_times.lock().await, 4);
         Ok(())
     }
+
+    #[tokio::test]
+    async fn test_fn_mut_when_and_notify() -> anyhow::Result<()> {
+        let mut calls_retryable: Vec<()> = vec![];
+        let mut calls_notify: Vec<()> = vec![];
+
+        let f = || async { Err::<(), anyhow::Error>(anyhow::anyhow!("retryable")) };
+
+        let backoff = ExponentialBuilder::default().with_min_delay(Duration::from_millis(1));
+        let result = f
+            .retry(&backoff)
+            .when(|_| {
+                calls_retryable.push(());
+                true
+            })
+            .notify(|_, _| {
+                calls_notify.push(());
+            })
+            .await;
+
+        assert!(result.is_err());
+        assert_eq!("retryable", result.unwrap_err().to_string());
+        // `f` always returns error "retryable", so it should be executed
+        // 4 times (retry 3 times).
+        assert_eq!(calls_retryable.len(), 4);
+        assert_eq!(calls_notify.len(), 3);
+        Ok(())
+    }
 }