diff --git a/Cargo.toml b/Cargo.toml
index f23886ddb..dff66841c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,6 @@ embed-resource = "1.1"
 [dependencies]
 base91 = { path = "base91" }
 bitflags = "1.0"
-boxfnonce = "0.1"
 clipboard = "0.5"
 dirs = "1.0"
 euclid = "0.19"
diff --git a/promise/Cargo.toml b/promise/Cargo.toml
index 5c2bf03ee..576be8f61 100644
--- a/promise/Cargo.toml
+++ b/promise/Cargo.toml
@@ -6,5 +6,4 @@ edition = "2018"
 
 [dependencies]
 failure = "0.1"
-boxfnonce = "0.1"
 rayon = "1.0"
diff --git a/promise/src/lib.rs b/promise/src/lib.rs
index bea31bf78..c03718642 100644
--- a/promise/src/lib.rs
+++ b/promise/src/lib.rs
@@ -1,9 +1,8 @@
-use boxfnonce::SendBoxFnOnce;
-use failure::Error;
+use failure::{Error, Fallible};
 use std::sync::{Arc, Condvar, Mutex};
 
-type NextFunc<T> = SendBoxFnOnce<'static, (Result<T, Error>,)>;
-pub type SpawnFunc = SendBoxFnOnce<'static, ()>;
+type NextFunc<T> = Box<dyn FnOnce(Fallible<T>) + Send>;
+pub type SpawnFunc = Box<dyn FnOnce() + Send>;
 
 pub trait Executor: Send {
     fn execute(&self, f: SpawnFunc);
@@ -32,7 +31,7 @@ impl RayonExecutor {
 
 impl Executor for RayonExecutor {
     fn execute(&self, f: SpawnFunc) {
-        rayon::spawn(|| f.call());
+        rayon::spawn(|| f());
     }
     fn clone_executor(&self) -> Box<Executor> {
         Box::new(RayonExecutor::new())
@@ -103,7 +102,7 @@ impl<T> Promise<T> {
             PromiseState::Waiting(core) => {
                 let mut locked = core.data.lock().unwrap();
                 match locked.propagate.take() {
-                    Some(func) => func.call(result),
+                    Some(func) => func(result),
                     None => locked.result = Some(result),
                 }
                 core.cond.notify_one();
@@ -153,10 +152,10 @@ impl<T: Send + 'static> Future<T> {
         let mut promise = Promise::new();
         let future = promise.get_future().unwrap();
 
-        let func = SendBoxFnOnce::from(f);
-        let promise_chain = NextFunc::from(move |result| promise.result(result));
-        executor.execute(SpawnFunc::from(move || {
-            let future = func.call().into();
+        let func = Box::new(f);
+        let promise_chain = Box::new(move |result| promise.result(result));
+        executor.execute(Box::new(move || {
+            let future = func().into();
             future.chain(promise_chain);
         }));
         future
@@ -165,12 +164,12 @@ impl<T: Send + 'static> Future<T> {
     fn chain(self, f: NextFunc<T>) {
         match self.state {
             FutureState::Ready(result) => {
-                f.call(result);
+                f(result);
             }
             FutureState::Waiting(core) => {
                 let mut locked = core.data.lock().unwrap();
                 if let Some(result) = locked.result.take() {
-                    f.call(result);
+                    f(result);
                 } else {
                     locked.propagate = Some(f);
                 }
@@ -207,12 +206,12 @@ impl<T: Send + 'static> Future<T> {
     {
         let mut promise = Promise::new();
         let future = promise.get_future().unwrap();
-        let func = SendBoxFnOnce::from(f);
+        let func = Box::new(f);
 
-        let promise_chain = NextFunc::from(move |result| promise.result(result));
+        let promise_chain = Box::new(move |result| promise.result(result));
 
-        self.chain(SendBoxFnOnce::from(move |result| {
-            let future = func.call(result).into();
+        self.chain(Box::new(move |result| {
+            let future = func(result).into();
             future.chain(promise_chain);
         }));
         future
@@ -233,13 +232,13 @@ impl<T: Send + 'static> Future<T> {
     {
         let mut promise = Promise::new();
         let future = promise.get_future().unwrap();
-        let func = SendBoxFnOnce::from(f);
+        let func = Box::new(f);
 
-        let promise_chain = NextFunc::from(move |result| promise.result(result));
+        let promise_chain = Box::new(move |result| promise.result(result));
 
-        self.chain(SendBoxFnOnce::from(move |result| {
+        self.chain(Box::new(move |result| {
             let future = match result {
-                Ok(value) => func.call(value).into(),
+                Ok(value) => func(value).into(),
                 Err(err) => Err(err).into(),
             };
             future.chain(promise_chain);
@@ -261,14 +260,14 @@ impl<T: Send + 'static> Future<T> {
     {
         let mut promise = Promise::new();
         let future = promise.get_future().unwrap();
-        let func = SendBoxFnOnce::from(f);
+        let func = Box::new(f);
 
-        let promise_chain = NextFunc::from(move |result| promise.result(result));
+        let promise_chain = Box::new(move |result| promise.result(result));
 
-        self.chain(SendBoxFnOnce::from(move |result| {
+        self.chain(Box::new(move |result| {
             let future = match result {
                 Ok(value) => Ok(value).into(),
-                Err(err) => func.call(err).into(),
+                Err(err) => func(err).into(),
             };
             future.chain(promise_chain);
         }));
diff --git a/src/frontend/glium/glutinloop.rs b/src/frontend/glium/glutinloop.rs
index ca240d046..06e112b2e 100644
--- a/src/frontend/glium/glutinloop.rs
+++ b/src/frontend/glium/glutinloop.rs
@@ -329,7 +329,7 @@ impl GuiEventLoop {
 
     fn process_gui_exec(&self) -> Result<(), Error> {
         while let Some(func) = self.gui_thread_sends.borrow_mut().pop_front() {
-            func.call();
+            func();
         }
 
         let start = SystemTime::now();
@@ -344,7 +344,7 @@ impl GuiEventLoop {
                 _ => {}
             }
             match self.gui_rx.try_recv() {
-                Ok(func) => func.call(),
+                Ok(func) => func(),
                 Err(TryRecvError::Empty) => return Ok(()),
                 Err(err) => bail!("poll_rx disconnected {:?}", err),
             }
diff --git a/src/frontend/muxserver/mod.rs b/src/frontend/muxserver/mod.rs
index c701064cf..af9b6cb4e 100644
--- a/src/frontend/muxserver/mod.rs
+++ b/src/frontend/muxserver/mod.rs
@@ -62,7 +62,7 @@ impl FrontEnd for MuxServerFrontEnd {
     fn run_forever(&self) -> Result<(), Error> {
         loop {
             match self.rx.recv() {
-                Ok(func) => func.call(),
+                Ok(func) => func(),
                 Err(err) => bail!("while waiting for events: {:?}", err),
             }
 
diff --git a/src/frontend/xwindows/x11loop.rs b/src/frontend/xwindows/x11loop.rs
index f29c8a0f2..8a64a9a00 100644
--- a/src/frontend/xwindows/x11loop.rs
+++ b/src/frontend/xwindows/x11loop.rs
@@ -248,7 +248,7 @@ impl GuiEventLoop {
 
     fn process_gui_exec(&self) -> Result<(), Error> {
         match self.gui_rx.try_recv() {
-            Ok(func) => func.call(),
+            Ok(func) => func(),
             Err(TryRecvError::Empty) => return Ok(()),
             Err(err) => bail!("poll_rx disconnected {:?}", err),
         }