diff --git a/ostd/channel.hh b/ostd/channel.hh
index 26817f5..7c851e0 100644
--- a/ostd/channel.hh
+++ b/ostd/channel.hh
@@ -6,7 +6,8 @@
 #ifndef OSTD_CHANNEL_HH
 #define OSTD_CHANNEL_HH
 
-#include <stdio.h>
+#include <type_traits>
+#include <algorithm>
 #include <list>
 #include <mutex>
 #include <condition_variable>
@@ -19,10 +20,8 @@ struct channel_error: std::logic_error {
     using std::logic_error::logic_error;
 };
 
-template<typename T, typename C = std::condition_variable>
+template<typename T>
 struct channel {
-    using condition_variable_type = C;
-
     /* default ctor works for default C */
     channel(): p_state(new impl) {}
 
@@ -67,11 +66,68 @@ struct channel {
     }
 
 private:
+    struct cond_iface {
+        cond_iface() {}
+        virtual ~cond_iface() {}
+        virtual void notify_one() = 0;
+        virtual void notify_all() = 0;
+        virtual void wait(std::unique_lock<std::mutex> &) = 0;
+    };
+
+    template<typename C>
+    struct cond_impl: cond_iface {
+        cond_impl(): p_cond() {}
+        template<typename F>
+        cond_impl(F &func): p_cond(func()) {}
+        void notify_one() {
+            p_cond.notify_one();
+        }
+        void notify_all() {
+            p_cond.notify_all();
+        }
+        void wait(std::unique_lock<std::mutex> &l) {
+            p_cond.wait(l);
+        }
+    private:
+        C p_cond;
+    };
+
+    struct cond {
+        cond() {
+            new (reinterpret_cast<void *>(&p_condbuf))
+                cond_impl<std::condition_variable>();
+        }
+        template<typename F>
+        cond(F &func) {
+            new (reinterpret_cast<void *>(&p_condbuf))
+                cond_impl<std::result_of_t<F()>>(func);
+        }
+        ~cond() {
+            reinterpret_cast<cond_iface *>(&p_condbuf)->~cond_iface();
+        }
+
+        void notify_one() {
+            reinterpret_cast<cond_iface *>(&p_condbuf)->notify_one();
+        }
+        void notify_all() {
+            reinterpret_cast<cond_iface *>(&p_condbuf)->notify_all();
+        }
+        void wait(std::unique_lock<std::mutex> &l) {
+            reinterpret_cast<cond_iface *>(&p_condbuf)->wait(l);
+        }
+
+    private:
+        std::aligned_storage_t<std::max(
+            6 * sizeof(void *), sizeof(cond_impl<std::condition_variable>)
+        ), alignof(std::condition_variable)> p_condbuf;
+    };
+
     struct impl {
-        impl() {}
+        impl() {
+        }
 
         template<typename F>
-        impl(F &func): p_lock(), p_cond(func()) {}
+        impl(F &func): p_lock(), p_cond(func) {}
 
         template<typename U>
         void put(U &&val) {
@@ -118,7 +174,7 @@ private:
 
         std::list<T> p_messages;
         mutable std::mutex p_lock;
-        C p_cond;
+        cond p_cond;
         bool p_closed = false;
     };
 
diff --git a/ostd/concurrency.hh b/ostd/concurrency.hh
index 6016feb..5319eba 100644
--- a/ostd/concurrency.hh
+++ b/ostd/concurrency.hh
@@ -19,9 +19,6 @@
 namespace ostd {
 
 struct thread_scheduler {
-    template<typename T>
-    using channel_type = channel<T>;
-
     ~thread_scheduler() {
         join_all();
     }
@@ -174,9 +171,6 @@ private:
     };
 
 public:
-    template<typename T>
-    using channel_type = channel<T, coro_cond>;
-
     basic_simple_coroutine_scheduler(
         size_t ss = TR::default_size(),
         size_t cs = basic_stack_pool<TR, Protected>::DEFAULT_CHUNK_SIZE
@@ -228,8 +222,8 @@ public:
     }
 
     template<typename T>
-    channel<T, coro_cond> make_channel() {
-        return channel<T, coro_cond>{[this]() {
+    channel<T> make_channel() {
+        return channel<T>{[this]() {
             return coro_cond{*this};
         }};
     }
@@ -354,9 +348,6 @@ private:
     };
 
 public:
-    template<typename T>
-    using channel_type = channel<T, task_cond>;
-
     basic_coroutine_scheduler(
         size_t ss = TR::default_size(),
         size_t cs = basic_stack_pool<TR, Protected>::DEFAULT_CHUNK_SIZE
@@ -409,8 +400,8 @@ public:
     }
 
     template<typename T>
-    channel<T, task_cond> make_channel() {
-        return channel<T, task_cond>{[this]() {
+    channel<T> make_channel() {
+        return channel<T>{[this]() {
             return task_cond{*this};
         }};
     }
@@ -551,7 +542,7 @@ inline void yield(S &sched) {
 }
 
 template<typename T, typename S>
-inline auto make_channel(S &sched) -> typename S::template channel_type<T> {
+inline channel<T> make_channel(S &sched) {
     return sched.template make_channel<T>();
 }
 
diff --git a/ostd/thread_pool.hh b/ostd/thread_pool.hh
index 0a54b50..ada48b2 100644
--- a/ostd/thread_pool.hh
+++ b/ostd/thread_pool.hh
@@ -60,7 +60,7 @@ namespace detail {
 
         template<typename F>
         tpool_func(F &&func) {
-            if (sizeof(F) <= sizeof(p_buf)) {
+            if (sizeof(tpool_func_impl<F>) <= sizeof(p_buf)) {
                 p_func = ::new(reinterpret_cast<void *>(&p_buf))
                     tpool_func_impl<F>{std::move(func)};
             } else {
@@ -81,7 +81,7 @@ namespace detail {
         }
     private:
         std::aligned_storage_t<
-            sizeof(std::packaged_task<void()>) + sizeof(void *)
+            sizeof(tpool_func_impl<std::packaged_task<void()>>)
         > p_buf;
         tpool_func_base *p_func;
     };