diff --git a/include/boost/fiber/algorithm.hpp b/include/boost/fiber/algorithm.hpp
index 5ae4dcfb..3aa56001 100644
--- a/include/boost/fiber/algorithm.hpp
+++ b/include/boost/fiber/algorithm.hpp
@@ -29,6 +29,8 @@ namespace fibers {
 
 struct BOOST_FIBERS_DECL algorithm : private noncopyable
 {
+    virtual void add( detail::fiber_base::ptr_t const&) = 0;
+
     virtual void priority( detail::fiber_base::ptr_t const&, int) = 0;
 
     virtual void join( detail::fiber_base::ptr_t const&) = 0;
@@ -41,10 +43,6 @@ struct BOOST_FIBERS_DECL algorithm : private noncopyable
 
     virtual void yield() = 0;
 
-    virtual void migrate_to( fiber const&) = 0;
-
-    virtual fiber steel_from() = 0;
-
     virtual ~algorithm() {}
 };
 
diff --git a/include/boost/fiber/fiber.hpp b/include/boost/fiber/fiber.hpp
index 4be7861c..5a85d93f 100644
--- a/include/boost/fiber/fiber.hpp
+++ b/include/boost/fiber/fiber.hpp
@@ -53,7 +53,7 @@ private:
     typedef base_t::ptr_t         ptr_t;
     typedef void ( dummy::*safe_bool)();
 
-    static void spawn_( fiber &);
+    static void spawn_( detail::fiber_base::ptr_t const&);
 
     ptr_t       impl_;
 
@@ -66,7 +66,7 @@ public:
         impl_()
     {}
 
-    fiber( ptr_t const& impl) BOOST_NOEXCEPT :
+    explicit fiber( ptr_t const& impl) BOOST_NOEXCEPT :
         impl_( impl)
     {}
 
@@ -86,7 +86,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< fiber_fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename StackAllocator >
@@ -102,7 +102,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< fiber_fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename StackAllocator, typename Allocator >
@@ -118,7 +118,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< fiber_fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 #endif
     template< typename Fn >
@@ -138,7 +138,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< Fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn, typename StackAllocator >
@@ -158,7 +158,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< Fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
     template< typename Fn, typename StackAllocator, typename Allocator >
     explicit fiber( BOOST_RV_REF( Fn) fn, attributes const& attr,
@@ -177,7 +177,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( forward< Fn >( fn), attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 #else
     template< typename Fn >
@@ -197,7 +197,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn, typename StackAllocator >
@@ -217,7 +217,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn, typename StackAllocator, typename Allocator >
@@ -237,7 +237,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn >
@@ -257,7 +257,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn, typename StackAllocator >
@@ -277,7 +277,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 
     template< typename Fn, typename StackAllocator, typename Allocator >
@@ -297,7 +297,7 @@ public:
         impl_ = ptr_t(
             // placement new
             ::new( a.allocate( 1) ) object_t( fn, attr, stack_alloc, a) );
-        spawn_( * this);
+        spawn_( impl_);
     }
 #endif
 
@@ -317,19 +317,13 @@ public:
     }
 
     operator safe_bool() const BOOST_NOEXCEPT
-    { return ( ! empty() && ! impl_->is_terminated() ) ? & dummy::nonnull : 0; }
+    { return joinable() ? & dummy::nonnull : 0; }
 
     bool operator!() const BOOST_NOEXCEPT
-    { return empty() || impl_->is_terminated(); }
-
-    void swap( fiber & other) BOOST_NOEXCEPT
-    { impl_.swap( other.impl_); }
-
-    bool empty() const BOOST_NOEXCEPT
-    { return 0 == impl_.get(); }
+    { return ! joinable(); }
 
     bool joinable() const BOOST_NOEXCEPT
-    { return ! empty(); }
+    { return impl_ && ! impl_->is_terminated(); }
 
     id get_id() const BOOST_NOEXCEPT
     { return impl_ ? impl_->get_id() : id(); }
@@ -344,6 +338,9 @@ public:
     void join();
 
     void interrupt() BOOST_NOEXCEPT;
+
+    void swap( fiber & other) BOOST_NOEXCEPT
+    { impl_.swap( other.impl_); }
 };
 
 inline
diff --git a/include/boost/fiber/round_robin.hpp b/include/boost/fiber/round_robin.hpp
index f1588146..2718cec6 100644
--- a/include/boost/fiber/round_robin.hpp
+++ b/include/boost/fiber/round_robin.hpp
@@ -12,6 +12,7 @@
 
 #include <boost/assert.hpp>
 #include <boost/config.hpp>
+#include <boost/move/move.hpp>
 #include <boost/thread/locks.hpp>
 
 #include <boost/fiber/detail/config.hpp>
@@ -49,6 +50,8 @@ public:
 
     ~round_robin() BOOST_NOEXCEPT;
 
+    void add( detail::fiber_base::ptr_t const&);
+
     void priority( detail::fiber_base::ptr_t const&, int);
 
     void join( detail::fiber_base::ptr_t const&);
@@ -62,7 +65,7 @@ public:
 
     void yield();
 
-    void migrate_to( fiber const&);
+    void migrate_to( BOOST_RV_REF( fiber) f);
 
     fiber steel_from();
 };
diff --git a/src/fiber.cpp b/src/fiber.cpp
index 59a0cf48..9fe0a09a 100644
--- a/src/fiber.cpp
+++ b/src/fiber.cpp
@@ -25,8 +25,8 @@ namespace boost {
 namespace fibers {
 
 void
-fiber::spawn_( fiber & f)
-{ detail::scheduler::instance().migrate_to( f); }
+fiber::spawn_( detail::fiber_base::ptr_t const& f)
+{ detail::scheduler::instance().add( f); }
 
 int
 fiber::priority() const
diff --git a/src/mutex.cpp b/src/mutex.cpp
index 98cdbb9f..0c3a770b 100644
--- a/src/mutex.cpp
+++ b/src/mutex.cpp
@@ -34,7 +34,7 @@ mutex::lock()
 {
     while ( LOCKED == state_.exchange( LOCKED, memory_order_seq_cst) )
     {
-        BOOST_ASSERT( this_fiber::is_fiberized() );
+        if ( ! this_fiber::is_fiberized() ) ::abort();
 
         unique_lock< detail::spinlock > lk( waiting_mtx_);
         waiting_.push_back(
diff --git a/src/round_robin.cpp b/src/round_robin.cpp
index 7a36f417..a2fdbbbc 100644
--- a/src/round_robin.cpp
+++ b/src/round_robin.cpp
@@ -54,6 +54,16 @@ round_robin::~round_robin()
 #endif
 }
 
+void
+round_robin::add( detail::fiber_base::ptr_t const& f)
+{
+    BOOST_ASSERT( f);
+    BOOST_ASSERT( ! f->is_running() );
+    BOOST_ASSERT( ! f->is_terminated() );
+
+    wqueue_.push_back( f);
+}
+
 bool
 round_robin::run()
 {
@@ -218,14 +228,9 @@ round_robin::priority( detail::fiber_base::ptr_t const& f, int prio)
 }
 
 void
-round_robin::migrate_to( fiber const& f_)
+round_robin::migrate_to( BOOST_RV_REF( fiber) f)
 {
-    detail::fiber_base::ptr_t f = detail::scheduler::extract( f_);
-    BOOST_ASSERT( f);
-    BOOST_ASSERT( ! f->is_running() );
-    BOOST_ASSERT( ! f->is_terminated() );
-
-    wqueue_.push_back( f);
+    add( detail::scheduler::extract( f) );
 }
 
 fiber
diff --git a/test/test_fiber_steeling.cpp b/test/test_fiber_steeling.cpp
index a07d2d40..af9e055c 100644
--- a/test/test_fiber_steeling.cpp
+++ b/test/test_fiber_steeling.cpp
@@ -89,10 +89,10 @@ void fn_steel_fibers( boost::fibers::round_robin * other_ds, boost::barrier * b,
         if ( f)
         {
             ++( * count);
-            ds.migrate_to( f);
+            ds.migrate_to( boost::move( f) );
             while ( boost::fibers::run() );
         }
-        f.detach();
+        BOOST_ASSERT( ! f);
     }
 }