diff --git a/artiq/runtime.rs/src/kernel_proto.rs b/artiq/runtime.rs/src/kernel_proto.rs
index b84a93df0..64a074518 100644
--- a/artiq/runtime.rs/src/kernel_proto.rs
+++ b/artiq/runtime.rs/src/kernel_proto.rs
@@ -110,7 +110,7 @@ impl<'a> Message<'a> {
                 let msg = c::RpcRecvReply {
                     ty: c::Type::RpcRecvReply,
                     alloc_size: alloc_size as _,
-                    exception: exn.map_or(ptr::null(), |exn| &exn as *const _)
+                    exception: exn.as_ref().map_or(ptr::null(), |exn| exn as *const _)
                 };
                 f(&msg as *const _ as *const _)
             }
diff --git a/artiq/runtime.rs/src/session.rs b/artiq/runtime.rs/src/session.rs
index 2f04926d7..644381ea8 100644
--- a/artiq/runtime.rs/src/session.rs
+++ b/artiq/runtime.rs/src/session.rs
@@ -264,7 +264,36 @@ fn process_host_message(waiter: Waiter,
             Ok(())
         }
 
-        request => unexpected!("unexpected request {:?} from host machine", request)
+        host::Request::RpcException {
+            name, message, param, file, line, column, function
+        } => {
+            if session.kernel_state != KernelState::RpcWait {
+                unexpected!("unsolicited RPC reply")
+            }
+
+            try!(kern_recv(waiter, |reply| {
+                match reply {
+                    kern::RpcRecvRequest { .. } => Ok(()),
+                    other =>
+                        unexpected!("unexpected reply from kernel CPU: {:?}", other)
+                }
+            }));
+            try!(kern_send(waiter, kern::RpcRecvReply {
+                alloc_size: 0,
+                exception: Some(kern::Exception {
+                    name: &name,
+                    message: &message,
+                    param: param,
+                    file: &file,
+                    line: line,
+                    column: column,
+                    function: &function
+                })
+            }));
+
+            session.kernel_state = KernelState::Running;
+            Ok(())
+        }
     }
 }
 
diff --git a/artiq/runtime/Makefile b/artiq/runtime/Makefile
index 30a8b1d7f..0f8aec3cd 100644
--- a/artiq/runtime/Makefile
+++ b/artiq/runtime/Makefile
@@ -15,8 +15,8 @@ CFLAGS += -I$(LIBALLOC_DIRECTORY) \
 	-I$(LIBUNWIND_DIRECTORY) \
 	-I$(LIBUNWIND_DIRECTORY)/../unwinder/include \
 	-I$(LIBLWIP_DIRECTORY)/../lwip/src/include \
-	-I$(LIBLWIP_DIRECTORY) \
-	-DNDEBUG
+	-I$(LIBLWIP_DIRECTORY)
+CFLAGS += -DNDEBUG
 
 all: runtime.bin runtime.fbi