diff --git a/actix-service/CHANGES.md b/actix-service/CHANGES.md
index cc9dd9ef..afd194f5 100644
--- a/actix-service/CHANGES.md
+++ b/actix-service/CHANGES.md
@@ -2,6 +2,9 @@
 
 ## [0.1.6] - 2019-01-xx
 
+### Changed
+
+* Use `FnMut` instead of `Fn` for .apply() and .map() combinators and `FnService` type
 
 ## [0.1.5] - 2019-01-13
 
diff --git a/actix-service/src/apply.rs b/actix-service/src/apply.rs
index e6624057..89d6559f 100644
--- a/actix-service/src/apply.rs
+++ b/actix-service/src/apply.rs
@@ -78,7 +78,7 @@ where
 impl<T, F, In, Out, Request> ApplyNewService<T, F, In, Out, Request>
 where
     T: NewService<Request>,
-    F: Fn(In, &mut T::Service) -> Out,
+    F: FnMut(In, &mut T::Service) -> Out,
     Out: IntoFuture,
     Out::Error: From<T::Error>,
 {
@@ -95,7 +95,7 @@ where
 impl<T, F, In, Out, Request> Clone for ApplyNewService<T, F, In, Out, Request>
 where
     T: NewService<Request> + Clone,
-    F: Fn(In, &mut T::Service) -> Out + Clone,
+    F: FnMut(In, &mut T::Service) -> Out + Clone,
     Out: IntoFuture,
 {
     fn clone(&self) -> Self {
@@ -110,7 +110,7 @@ where
 impl<T, F, In, Out, Request> NewService<In> for ApplyNewService<T, F, In, Out, Request>
 where
     T: NewService<Request>,
-    F: Fn(In, &mut T::Service) -> Out + Clone,
+    F: FnMut(In, &mut T::Service) -> Out + Clone,
     Out: IntoFuture,
     Out::Error: From<T::Error>,
 {
@@ -129,7 +129,7 @@ where
 pub struct ApplyNewServiceFuture<T, F, In, Out, Request>
 where
     T: NewService<Request>,
-    F: Fn(In, &mut T::Service) -> Out,
+    F: FnMut(In, &mut T::Service) -> Out,
     Out: IntoFuture,
 {
     fut: T::Future,
@@ -140,7 +140,7 @@ where
 impl<T, F, In, Out, Request> ApplyNewServiceFuture<T, F, In, Out, Request>
 where
     T: NewService<Request>,
-    F: Fn(In, &mut T::Service) -> Out,
+    F: FnMut(In, &mut T::Service) -> Out,
     Out: IntoFuture,
 {
     fn new(fut: T::Future, f: F) -> Self {
@@ -155,7 +155,7 @@ where
 impl<T, F, In, Out, Request> Future for ApplyNewServiceFuture<T, F, In, Out, Request>
 where
     T: NewService<Request>,
-    F: Fn(In, &mut T::Service) -> Out,
+    F: FnMut(In, &mut T::Service) -> Out,
     Out: IntoFuture,
     Out::Error: From<T::Error>,
 {
diff --git a/actix-service/src/lib.rs b/actix-service/src/lib.rs
index 1e033273..0d2e05d5 100644
--- a/actix-service/src/lib.rs
+++ b/actix-service/src/lib.rs
@@ -128,7 +128,7 @@ pub trait ServiceExt<Request>: Service<Request> {
     fn map<F, R>(self, f: F) -> Map<Self, F, R>
     where
         Self: Sized,
-        F: Fn(Self::Response) -> R,
+        F: FnMut(Self::Response) -> R,
     {
         Map::new(self, f)
     }
@@ -245,7 +245,7 @@ pub trait NewService<Request> {
     fn map<F, R>(self, f: F) -> MapNewService<Self, F, R>
     where
         Self: Sized,
-        F: Fn(Self::Response) -> R,
+        F: FnMut(Self::Response) -> R,
     {
         MapNewService::new(self, f)
     }
diff --git a/actix-service/src/map.rs b/actix-service/src/map.rs
index d3fb3c06..ac255ff1 100644
--- a/actix-service/src/map.rs
+++ b/actix-service/src/map.rs
@@ -18,7 +18,7 @@ impl<A, F, Response> Map<A, F, Response> {
     pub fn new<Request>(service: A, f: F) -> Self
     where
         A: Service<Request>,
-        F: Fn(A::Response) -> Response,
+        F: FnMut(A::Response) -> Response,
     {
         Self {
             service,
@@ -45,7 +45,7 @@ where
 impl<A, F, Request, Response> Service<Request> for Map<A, F, Response>
 where
     A: Service<Request>,
-    F: Fn(A::Response) -> Response + Clone,
+    F: FnMut(A::Response) -> Response + Clone,
 {
     type Response = Response;
     type Error = A::Error;
@@ -63,7 +63,7 @@ where
 pub struct MapFuture<A, F, Request, Response>
 where
     A: Service<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     f: F,
     fut: A::Future,
@@ -72,7 +72,7 @@ where
 impl<A, F, Request, Response> MapFuture<A, F, Request, Response>
 where
     A: Service<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     fn new(fut: A::Future, f: F) -> Self {
         MapFuture { f, fut }
@@ -82,7 +82,7 @@ where
 impl<A, F, Request, Response> Future for MapFuture<A, F, Request, Response>
 where
     A: Service<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     type Item = Response;
     type Error = A::Error;
@@ -107,7 +107,7 @@ impl<A, F, Response> MapNewService<A, F, Response> {
     pub fn new<Request>(a: A, f: F) -> Self
     where
         A: NewService<Request>,
-        F: Fn(A::Response) -> Response,
+        F: FnMut(A::Response) -> Response,
     {
         Self {
             a,
@@ -134,7 +134,7 @@ where
 impl<A, F, Request, Response> NewService<Request> for MapNewService<A, F, Response>
 where
     A: NewService<Request>,
-    F: Fn(A::Response) -> Response + Clone,
+    F: FnMut(A::Response) -> Response + Clone,
 {
     type Response = Response;
     type Error = A::Error;
@@ -151,7 +151,7 @@ where
 pub struct MapNewServiceFuture<A, F, Request, Response>
 where
     A: NewService<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     fut: A::Future,
     f: Option<F>,
@@ -160,7 +160,7 @@ where
 impl<A, F, Request, Response> MapNewServiceFuture<A, F, Request, Response>
 where
     A: NewService<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     fn new(fut: A::Future, f: F) -> Self {
         MapNewServiceFuture { f: Some(f), fut }
@@ -170,7 +170,7 @@ where
 impl<A, F, Request, Response> Future for MapNewServiceFuture<A, F, Request, Response>
 where
     A: NewService<Request>,
-    F: Fn(A::Response) -> Response,
+    F: FnMut(A::Response) -> Response,
 {
     type Item = Map<A::Service, F, Response>;
     type Error = A::InitError;