diff --git a/client/brewpi_gui.py b/client/brewpi_gui.py
index c9ef99f..7d8e349 100755
--- a/client/brewpi_gui.py
+++ b/client/brewpi_gui.py
@@ -659,8 +659,11 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.msg_sud.send({'Confirm': True})
 
 	def on_action_sud_new(self):
-		# Replaces the running Sud's schedule with an empty one, same as
-		# Load but with a built-in empty document instead of a file dialog.
+		# Sends an empty schedule via the same Load path Load Sud uses, with
+		# a built-in empty document instead of a file dialog - the server
+		# itself refuses this (like any Load) while a run is in progress,
+		# surfacing an error (see on_sud_changed()'s 'Error' handling)
+		# rather than the GUI trying to guess that here.
 		self.msg_sud.send({'Load': {'Name': '', 'Description': '', 'pot_mass': 0, 'pot_material': None, 'steps': []}})
 
 	def on_action_sud_save(self):
@@ -876,6 +879,8 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 					self.server_remaining_forecast = (anchor_min, forecast['T'], forecast['Theta'])
 			elif "Forecast" in key:
 				self.on_sud_forecast_received(msg['Forecast'])
+			elif "Error" in key:
+				QtWidgets.QMessageBox.warning(self, "Sud", msg['Error'])
 		self.update_sud_actions()
 
 	def on_sud_forecast_received(self, forecast):
diff --git a/tasks/sud.py b/tasks/sud.py
index ec38653..d9a3a43 100644
--- a/tasks/sud.py
+++ b/tasks/sud.py
@@ -196,6 +196,13 @@ class SudTask(ATask):
 					await self.send({'Name': self.sud.name, 'Description': self.sud.description})
 					await self.send({'Json': pair[1]})
 					await self.send_forecast(pair[1])
+				else:
+					# Sud.load() refuses while a run is in progress (state
+					# not IDLE/DONE) - tell the client why instead of
+					# silently dropping the request. The client has no
+					# business pre-emptively guessing this itself from its
+					# own (replicated, laggy) view of the state.
+					await self.send({'Error': 'Cannot load a new schedule while a run is in progress - stop it first.'})
 
 	async def send(self, data):
 		await self.msg_handler.send(data)