diff --git a/include/boost/process/v2/windows/default_launcher.hpp b/include/boost/process/v2/windows/default_launcher.hpp
index 16ff12d46..e84bbbdfb 100644
--- a/include/boost/process/v2/windows/default_launcher.hpp
+++ b/include/boost/process/v2/windows/default_launcher.hpp
@@ -109,7 +109,7 @@ inline std::false_type probe_on_error(
 
 template<typename Launcher, typename Init>
 inline auto probe_on_error(Launcher & launcher, Init && init, derived && )
-        -> std::is_same<error_code, decltype(init.on_error(launcher, std::declval<const filesystem::path &>(), std::declval<std::wstring &>(), std::declval<error_code&>()))>;
+        -> std::is_same<void, decltype(init.on_error(launcher, std::declval<const filesystem::path &>(), std::declval<std::wstring &>(), std::declval<error_code&>()))>;
 
 template<typename Launcher, typename Init>
 using has_on_error = decltype(probe_on_error(std::declval<Launcher&>(), std::declval<Init>(), derived{}));
@@ -151,7 +151,7 @@ inline std::false_type probe_on_success(
 
 template<typename Launcher, typename Init>
 inline auto probe_on_success(Launcher & launcher, Init && init, derived && )
-        -> std::is_same<error_code, decltype(init.on_success(launcher, std::declval<const filesystem::path &>(), std::declval<std::wstring &>()))>;
+        -> std::is_same<void, decltype(init.on_success(launcher, std::declval<const filesystem::path &>(), std::declval<std::wstring &>()))>;
 
 template<typename Launcher, typename Init>
 using has_on_success = decltype(probe_on_success(std::declval<Launcher&>(), std::declval<Init>(), derived{}));