diff --git a/artiq/coredevice/comm_kernel.py b/artiq/coredevice/comm_kernel.py
index f566c5ff8..37ffd2aeb 100644
--- a/artiq/coredevice/comm_kernel.py
+++ b/artiq/coredevice/comm_kernel.py
@@ -563,14 +563,6 @@ class CommKernel:
 
         try:
             result = service(*args, **kwargs)
-            logger.debug("rpc service: %d %r %r = %r",
-                         service_id, args, kwargs, result)
-
-            self._write_header(Request.RPCReply)
-            self._write_bytes(return_tags)
-            self._send_rpc_value(bytearray(return_tags),
-                                 result, result, service)
-            self._flush()
         except RPCReturnValueError as exn:
             raise
         except Exception as exn:
@@ -617,6 +609,14 @@ class CommKernel:
                 self._write_int32(-1)  # column not known
                 self._write_string(function)
             self._flush()
+        else:
+            logger.debug("rpc service: %d %r %r = %r",
+                         service_id, args, kwargs, result)
+            self._write_header(Request.RPCReply)
+            self._write_bytes(return_tags)
+            self._send_rpc_value(bytearray(return_tags),
+                                 result, result, service)
+            self._flush()
 
     def _serve_exception(self, embedding_map, symbolizer, demangler):
         name = self._read_string()