diff --git a/include/stdexec/__detail/__sender_adaptor_closure.hpp b/include/stdexec/__detail/__sender_adaptor_closure.hpp
index 102d1a56f..868cbcb5c 100644
--- a/include/stdexec/__detail/__sender_adaptor_closure.hpp
+++ b/include/stdexec/__detail/__sender_adaptor_closure.hpp
@@ -93,7 +93,8 @@ namespace STDEXEC {
       template <sender _Sender>
         requires __callable<_Fn, _Sender, _As...>
       STDEXEC_ATTRIBUTE(host, device, always_inline)
-      auto operator()(_Sender&& __sndr) && noexcept(__nothrow_callable<_Fn, _Sender, _As...>) {
+      constexpr auto
+        operator()(_Sender&& __sndr) && noexcept(__nothrow_callable<_Fn, _Sender, _As...>) {
         return STDEXEC::__apply(
           static_cast<_Fn&&>(__fn_),
           static_cast<__tuple<_As...>&&>(__args_),
@@ -103,7 +104,7 @@ namespace STDEXEC {
       template <sender _Sender>
         requires __callable<const _Fn&, _Sender, const _As&...>
       STDEXEC_ATTRIBUTE(host, device, always_inline)
-      auto operator()(_Sender&& __sndr) const & noexcept(
+      constexpr auto operator()(_Sender&& __sndr) const & noexcept(
         __nothrow_callable<const _Fn&, _Sender, const _As&...>) {
         return STDEXEC::__apply(__fn_, __args_, static_cast<_Sender&&>(__sndr));
       }
diff --git a/include/stdexec/__detail/__tuple.hpp b/include/stdexec/__detail/__tuple.hpp
index 52ce15d21..f6818d3fd 100644
--- a/include/stdexec/__detail/__tuple.hpp
+++ b/include/stdexec/__detail/__tuple.hpp
@@ -219,9 +219,10 @@ namespace STDEXEC {
         template <class... _Ts>
         using __tuple_t = __mcall<_CvRef, __tuple<_Ts...>>;
 
-        template <class... _Ts, class... _Us, __callable<_Us..., __mcall<_CvRef, _Ts>...> _Fn>
-        void operator()(_Fn&& __fn, __tuple_t<_Ts...>&& __tupl, _Us&&... __us) const
-          noexcept(__nothrow_callable<_Fn, _Us..., __mcall<_CvRef, _Ts>...>);
+        template <class... _Ts, class... _Us, __callable<_Us..., __mcall1<_CvRef, _Ts>...> _Fn>
+        auto operator()(_Fn&& __fn, __tuple_t<_Ts...>&& __tupl, _Us&&... __us) const
+          noexcept(__nothrow_callable<_Fn, _Us..., __mcall1<_CvRef, _Ts>...>)
+            -> __call_result_t<_Fn, _Us..., __mcall1<_CvRef, _Ts>...>;
       };
 
       template <class _Tuple>
@@ -232,7 +233,8 @@ namespace STDEXEC {
         requires __callable<__impl_t<_Tuple>, _Fn, _Tuple, _Us...>
       STDEXEC_ATTRIBUTE(always_inline, host, device)
       constexpr auto operator()(_Fn&& __fn, _Tuple&& __tupl, _Us&&... __us) const
-        noexcept(__nothrow_callable<__impl_t<_Tuple>, _Fn, _Tuple, _Us...>) -> decltype(auto) {
+        noexcept(__nothrow_callable<__impl_t<_Tuple>, _Fn, _Tuple, _Us...>)
+          -> __call_result_t<__impl_t<_Tuple>, _Fn, _Tuple, _Us...> {
         constexpr size_t __size = STDEXEC_REMOVE_REFERENCE(_Tuple)::__size;
 
         if constexpr (__size == 0) {