diff --git a/rfg_adc_plotter/io/sweep_parser_core.py b/rfg_adc_plotter/io/sweep_parser_core.py
index c84673f..fbb52c1 100644
--- a/rfg_adc_plotter/io/sweep_parser_core.py
+++ b/rfg_adc_plotter/io/sweep_parser_core.py
@@ -500,18 +500,27 @@ class SweepAssembler:
             self._reset_current()
             if event.ch is not None:
                 self._cur_channel = int(event.ch)
-                self._cur_channels.add(int(event.ch))
             return packet
 
+        point_ch = int(event.ch)
+        packet: Optional[SweepPacket] = None
         if self._cur_channel is None:
-            self._cur_channel = int(event.ch)
-        self._cur_channels.add(int(event.ch))
+            self._cur_channel = point_ch
+        elif point_ch != self._cur_channel:
+            if self._xs:
+                # Never mix channels in a single sweep packet: otherwise
+                # identical step indexes can overwrite each other.
+                packet = self.finalize_current()
+                self._reset_current()
+            self._cur_channel = point_ch
+
+        self._cur_channels.add(point_ch)
         self._xs.append(int(event.x))
         self._ys.append(float(event.y))
         if event.aux is not None:
             self._aux_1.append(float(event.aux[0]))
             self._aux_2.append(float(event.aux[1]))
-        return None
+        return packet
 
     def finalize_current(self) -> Optional[SweepPacket]:
         if not self._xs:
diff --git a/tests/test_sweep_parser_core.py b/tests/test_sweep_parser_core.py
index 3c99bd2..fb50cc7 100644
--- a/tests/test_sweep_parser_core.py
+++ b/tests/test_sweep_parser_core.py
@@ -315,6 +315,24 @@ class SweepParserCoreTests(unittest.TestCase):
         self.assertEqual(aux[0][1], 100.0)
         self.assertEqual(aux[1][2], 95.0)
 
+    def test_sweep_assembler_splits_packet_on_channel_switch(self):
+        assembler = SweepAssembler(fancy=False, apply_inversion=False)
+        self.assertIsNone(assembler.consume(PointEvent(ch=1, x=1, y=10.0)))
+        packet = assembler.consume(PointEvent(ch=2, x=1, y=20.0))
+        self.assertIsNotNone(packet)
+
+        sweep_1, info_1, aux_1 = packet
+        self.assertIsNone(aux_1)
+        self.assertEqual(info_1["ch"], 1)
+        self.assertEqual(info_1["chs"], [1])
+        self.assertAlmostEqual(float(sweep_1[1]), 10.0, places=6)
+
+        sweep_2, info_2, aux_2 = assembler.finalize_current()
+        self.assertIsNone(aux_2)
+        self.assertEqual(info_2["ch"], 2)
+        self.assertEqual(info_2["chs"], [2])
+        self.assertAlmostEqual(float(sweep_2[1]), 20.0, places=6)
+
 
 if __name__ == "__main__":
     unittest.main()