diff --git a/artiq/coredevice/comm_kernel.py b/artiq/coredevice/comm_kernel.py
index e829b2fc3..a847115ab 100644
--- a/artiq/coredevice/comm_kernel.py
+++ b/artiq/coredevice/comm_kernel.py
@@ -689,7 +689,12 @@ class CommKernel:
 
         if service_id == 0:
             def service(*values):
-                counter = 0
+                if embedding_map.expects_return:
+                    embedding_map.return_value = values[0]
+                    counter = 1
+                else:
+                    counter = 0
+
                 for obj in embedding_map.attributes_writeback:
                     old_val = obj["obj"]
                     if "fields" in obj:
diff --git a/artiq/coredevice/core.py b/artiq/coredevice/core.py
index 146baadce..a7ea27269 100644
--- a/artiq/coredevice/core.py
+++ b/artiq/coredevice/core.py
@@ -123,6 +123,10 @@ class Core:
 
         self._run_compiled(kernel_library, embedding_map)
 
+        # set by NAC3
+        if embedding_map.expects_return:
+            return embedding_map.return_value
+
     def _run_compiled(self, kernel_library, embedding_map):
         if self.first_run:
             self.comm.check_system_info()