diff --git a/software/control/camera_toupcam.py b/software/control/camera_toupcam.py
index 8b1c085ce..0e54eb45e 100644
--- a/software/control/camera_toupcam.py
+++ b/software/control/camera_toupcam.py
@@ -1128,6 +1128,15 @@ def _set_acquisition_mode_imp(self, acquisition_mode: CameraAcquisitionMode):
             raise ValueError(f"Do not know how to handle {acquisition_mode=}")
         self._camera.put_Option(toupcam.TOUPCAM_OPTION_TRIGGER, trigger_option_value)
 
+        if acquisition_mode == CameraAcquisitionMode.SOFTWARE_TRIGGER:
+            # The SDK moves the trigger source to software along with the option only while the stream runs.
+            # Switched while stopped, the source stays on the hardware input (GPIO0) and every software
+            # trigger is ignored, so set it explicitly, as the hardware branch below does for its source.
+            try:
+                self._camera.IoControl(1, toupcam.TOUPCAM_IOCONTROLTYPE_SET_TRIGGERSOURCE, 5)  # 5 => software
+            except toupcam.HRESULTException as ex:
+                self._log.warning("Unable to set trigger source to software: " + hresult_checker(ex))
+
         if acquisition_mode == CameraAcquisitionMode.HARDWARE_TRIGGER:
             if HARDWARE_TRIGGER_MODE == HardwareTriggerMode.LEVEL:
                 try:
diff --git a/software/tests/control/test_camera_toupcam_trigger_source.py b/software/tests/control/test_camera_toupcam_trigger_source.py
new file mode 100644
index 000000000..85544767d
--- /dev/null
+++ b/software/tests/control/test_camera_toupcam_trigger_source.py
@@ -0,0 +1,61 @@
+"""Regression test: switching the ToupTek camera to software trigger while its stream is stopped.
+
+Measured on an ITR3CMOS26000KMA: the SDK moves the trigger source (IOCONTROLTYPE TRIGGERSOURCE: 1 = GPIO0,
+5 = software) along with OPTION_TRIGGER only while the stream runs. Switched from hardware to software
+trigger while stopped, the source stays on GPIO0 and every software trigger is ignored, which aborted
+Record + Z-Stack z-stacks started from hardware-trigger live view. The fake SDK below models that.
+"""
+
+import squid.logging
+from squid.abc import CameraAcquisitionMode
+import control.camera_toupcam as camera_toupcam
+import control.toupcam as toupcam
+
+_GPIO0, _SOFTWARE = 1, 5
+
+
+class _FakeSDK:
+    def __init__(self):
+        self.streaming = False
+        self.option_trigger = 1
+        self.source = _SOFTWARE
+
+    def put_Option(self, option, value):
+        if option == toupcam.TOUPCAM_OPTION_TRIGGER:
+            self.option_trigger = value
+            if self.streaming and value == 1:
+                self.source = _SOFTWARE  # the SDK follows the option only while streaming
+
+    def IoControl(self, line, kind, value):
+        if kind == toupcam.TOUPCAM_IOCONTROLTYPE_SET_TRIGGERSOURCE:
+            self.source = value
+        return 0
+
+
+def _make_camera():
+    cam = object.__new__(camera_toupcam.ToupcamCamera)
+    cam._camera = _FakeSDK()
+    cam._log = squid.logging.get_logger("test_toupcam_trigger_source")
+    cam.get_exposure_time = lambda: 20.0
+    cam.set_exposure_time = lambda exposure_ms: None
+    return cam
+
+
+def test_software_trigger_set_while_stopped_moves_the_source_off_the_hardware_input():
+    cam = _make_camera()
+    cam._set_acquisition_mode_imp(CameraAcquisitionMode.HARDWARE_TRIGGER)
+    assert cam._camera.source == _GPIO0
+
+    cam._camera.streaming = False
+    cam._set_acquisition_mode_imp(CameraAcquisitionMode.SOFTWARE_TRIGGER)
+
+    assert cam._camera.option_trigger == 1
+    assert cam._camera.source == _SOFTWARE
+
+
+def test_hardware_trigger_still_selects_the_hardware_input():
+    cam = _make_camera()
+    cam._set_acquisition_mode_imp(CameraAcquisitionMode.SOFTWARE_TRIGGER)
+    cam._set_acquisition_mode_imp(CameraAcquisitionMode.HARDWARE_TRIGGER)
+    assert cam._camera.option_trigger == 2
+    assert cam._camera.source == _GPIO0