diff --git a/src/thread/thread_d.hpp b/src/thread/thread_d.hpp
index f2855d8..bb7370f 100644
--- a/src/thread/thread_d.hpp
+++ b/src/thread/thread_d.hpp
@@ -665,6 +665,9 @@ namespace fc {
           if( tp <= (time_point::now()+fc::microseconds(10000)) ) 
             return;
 
+          FC_ASSERT(std::current_exception() == std::exception_ptr(), 
+                    "Attempting to yield while processing an exception");
+
           if( !current ) 
             current = new fc::context(&fc::thread::current());
 
@@ -698,6 +701,9 @@ namespace fc {
           if( p->ready() ) 
             return;
 
+          FC_ASSERT(std::current_exception() == std::exception_ptr(), 
+                    "Attempting to yield while processing an exception");
+
           if( timeout < time_point::now() ) 
             FC_THROW_EXCEPTION( timeout_exception, "" );