diff --git a/src/lib.rs b/src/lib.rs
index 8faf63e..21fe826 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,4 @@
-#![feature(fn_traits, unboxed_closures)]
+#![feature(fn_traits, unboxed_closures, tuple_trait)]
 
 //! Mocking framework for Rust (currently only nightly)
 //!
diff --git a/src/mock_store.rs b/src/mock_store.rs
index 22df3f0..58761ad 100644
--- a/src/mock_store.rs
+++ b/src/mock_store.rs
@@ -2,6 +2,7 @@ use crate::mocking::MockResult;
 use std::any::TypeId;
 use std::cell::RefCell;
 use std::collections::HashMap;
+use std::marker::Tuple;
 use std::mem::transmute;
 use std::rc::Rc;
 
@@ -44,7 +45,10 @@ impl MockStore {
             .add(id, mock);
     }
 
-    pub unsafe fn call<I, O>(&self, id: TypeId, mut input: I) -> MockResult<I, O> {
+    pub unsafe fn call<I, O>(&self, id: TypeId, mut input: I) -> MockResult<I, O>
+    where
+        I: Tuple,
+    {
         // Do not hold RefCell borrow while calling mock, it can try to modify mocks
         let layer_count = self.layers.borrow().len();
         for layer_idx in (0..layer_count).rev() {
@@ -118,7 +122,10 @@ struct ErasedStoredMock {
 }
 
 impl ErasedStoredMock {
-    unsafe fn call<I, O>(self, input: I) -> MockLayerResult<I, O> {
+    unsafe fn call<I, O>(self, input: I) -> MockLayerResult<I, O>
+    where
+        I: Tuple,
+    {
         let unerased: StoredMock<I, O> = transmute(self.mock);
         unerased.call(input)
     }
@@ -137,7 +144,10 @@ impl<I, O> StoredMock<I, O> {
         }
     }
 
-    fn call(&self, input: I) -> MockLayerResult<I, O> {
+    fn call(&self, input: I) -> MockLayerResult<I, O>
+    where
+        I: Tuple,
+    {
         match self.mock.try_borrow_mut() {
             Ok(mut mock) => MockLayerResult::Handled(mock.call_mut(input)),
             Err(_) => MockLayerResult::Unhandled(input),
diff --git a/src/mocking.rs b/src/mocking.rs
index f394a1e..c979276 100644
--- a/src/mocking.rs
+++ b/src/mocking.rs
@@ -1,6 +1,6 @@
 use crate::mock_store::{MockLayer, MockStore};
 use std::any::{Any, TypeId};
-use std::marker::PhantomData;
+use std::marker::{PhantomData, Tuple};
 use std::mem::transmute;
 
 /// Trait for setting up mocks
@@ -42,7 +42,9 @@ pub trait Mockable<T, O> {
     ///     assert_eq!("mocked", get_string(&Context::default()));
     /// }
     /// ```
-    unsafe fn mock_raw<M: FnMut<T, Output = MockResult<T, O>>>(&self, mock: M);
+    unsafe fn mock_raw<M: FnMut<T, Output = MockResult<T, O>>>(&self, mock: M)
+    where
+        T: Tuple;
 
     /// A safe variant of [mock_raw](#tymethod.mock_raw) for static closures
     ///
@@ -62,7 +64,9 @@ pub trait Mockable<T, O> {
     ///     assert_eq!("mocked", get_string());
     /// }
     /// ```
-    fn mock_safe<M: FnMut<T, Output = MockResult<T, O>> + 'static>(&self, mock: M);
+    fn mock_safe<M: FnMut<T, Output = MockResult<T, O>> + 'static>(&self, mock: M)
+    where
+        T: Tuple;
 
     /// Stop mocking this function.
     ///
@@ -97,7 +101,10 @@ pub fn clear_mocks() {
     MOCK_STORE.with(|mock_store| mock_store.clear())
 }
 
-impl<T, O, F: FnOnce<T, Output = O>> Mockable<T, O> for F {
+impl<T, O, F: FnOnce<T, Output = O>> Mockable<T, O> for F
+where
+    T: Tuple,
+{
     unsafe fn mock_raw<M: FnMut<T, Output = MockResult<T, O>>>(&self, mock: M) {
         let id = self.get_mock_id();
         let boxed = Box::new(mock) as Box<dyn FnMut<_, Output = _>>;
@@ -190,6 +197,7 @@ impl<'a> MockContext<'a> {
     where
         F: Mockable<I, O>,
         M: FnMut<I, Output = MockResult<I, O>> + 'a,
+        I: Tuple,
     {
         unsafe { self.mock_raw(mockable, mock) }
     }
@@ -202,6 +210,7 @@ impl<'a> MockContext<'a> {
     where
         F: Mockable<I, O>,
         M: FnMut<I, Output = MockResult<I, O>>,
+        I: Tuple,
     {
         let mock_box = Box::new(mock) as Box<dyn FnMut<_, Output = _>>;
         let mock_box_static: Box<dyn FnMut<I, Output = MockResult<I, O>> + 'static> =
diff --git a/tests/injecting.rs b/tests/injecting.rs
index 7767915..ba56594 100644
--- a/tests/injecting.rs
+++ b/tests/injecting.rs
@@ -1,4 +1,4 @@
-#![feature(const_fn, proc_macro_hygiene)]
+#![feature(proc_macro_hygiene)]
 
 // Test if injecting works even if mocktopus is aliased
 extern crate mocktopus as mocktopus_aliased;