diff --git a/core/src/main.py b/core/src/main.py
index 55e312125e..c22847e6e4 100644
--- a/core/src/main.py
+++ b/core/src/main.py
@@ -71,13 +71,13 @@ def _boot_apps() -> None:
 
 from trezor import loop, wire, workflow
 
-while True:
-    # initialize the wire codec
-    wire.setup(usb.iface_wire)
-    if __debug__:
-        wire.setup(usb.iface_debug)
+# initialize the wire codec
+wire.setup(usb.iface_wire)
+if __debug__:
+    wire.setup(usb.iface_debug)
 
-    _boot_apps()
-    loop.run()
+_boot_apps()
+loop.run()
 
-    # loop is empty, reboot
+# loop is empty. That should not happen
+utils.halt("All tasks have died.")
diff --git a/core/src/trezor/workflow.py b/core/src/trezor/workflow.py
index aaecf4a463..9cc10fe1c0 100644
--- a/core/src/trezor/workflow.py
+++ b/core/src/trezor/workflow.py
@@ -104,11 +104,14 @@ def _finalize_default(task: loop.Task, value: Any) -> None:
             log.debug(__name__, "default closed: %s", task)
         default_task = None
 
-        if not tasks and default_constructor:
+        if not tasks:
             # No registered workflows are running and we are in the default task
             # finalizer, so when this function finished, nothing will be running.
             # We must schedule a new instance of the default now.
-            start_default(default_constructor)
+            if default_constructor is not None:
+                start_default(default_constructor)
+            else:
+                raise RuntimeError  # no tasks and no default constructor
 
     else:
         if __debug__: