diff --git a/include/boost/fiber/fiber.hpp b/include/boost/fiber/fiber.hpp
index 418d032a..577cf8dc 100644
--- a/include/boost/fiber/fiber.hpp
+++ b/include/boost/fiber/fiber.hpp
@@ -137,7 +137,9 @@ public:
 
     template< typename PROPS >
     PROPS & properties() {
-        return dynamic_cast< PROPS & >( * impl_->get_properties() );
+        fiber_properties* props = impl_->get_properties();
+        BOOST_ASSERT_MSG(props, "fiber::properties not set");
+        return dynamic_cast< PROPS & >( * props );
     }
 };
 
diff --git a/include/boost/fiber/operations.hpp b/include/boost/fiber/operations.hpp
index f79a8236..0d54589d 100644
--- a/include/boost/fiber/operations.hpp
+++ b/include/boost/fiber/operations.hpp
@@ -10,6 +10,7 @@
 #include <mutex> // std::unique_lock
 
 #include <boost/config.hpp> 
+#include <boost/assert.hpp>
 
 #include <boost/fiber/detail/config.hpp>
 #include <boost/fiber/detail/scheduler.hpp>
@@ -51,7 +52,10 @@ void sleep_for( std::chrono::duration< Rep, Period > const& timeout_duration) {
 
 template< typename PROPS >
 PROPS & properties() {
-    return dynamic_cast< PROPS & >( * fibers::detail::scheduler::instance()->active()->get_properties() );
+    fibers::fiber_properties* props =
+        fibers::detail::scheduler::instance()->active()->get_properties();
+    BOOST_ASSERT_MSG(props, "this_fiber::properties not set");
+    return dynamic_cast< PROPS & >( * props );
 }
 
 } // this_fiber