diff --git a/pslab/instrument/buffer.py b/pslab/instrument/buffer.py
index a2a5cdb..565f8ba 100644
--- a/pslab/instrument/buffer.py
+++ b/pslab/instrument/buffer.py
@@ -69,19 +69,19 @@ def fill_buffer(self, data: list[int], starting_position: int = 0):
             start at the beginning of the buffer.
         """
         buf_size = 128
-        idx = starting_position
+        offset = 0
         remaining = len(data)
 
         while remaining > 0:
             self._device.send_byte(CP.COMMON)
             self._device.send_byte(CP.FILL_BUFFER)
-            self._device.send_int(idx)
+            self._device.send_int(starting_position + offset)
             samps = min(remaining, buf_size)
             self._device.send_int(samps)
 
-            for value in data[idx : idx + samps]:
+            for value in data[offset : offset + samps]:
                 self._device.send_int(value)
 
             self._device.get_ack()
-            idx += samps
+            offset += samps
             remaining -= samps
diff --git a/tests/test_buffer_fill.py b/tests/test_buffer_fill.py
new file mode 100644
index 0000000..2c81207
--- /dev/null
+++ b/tests/test_buffer_fill.py
@@ -0,0 +1,56 @@
+"""ADC buffer destinations must not skip values in the input data."""
+
+from unittest.mock import Mock, call
+
+import pytest
+
+import pslab.protocol as CP
+from pslab.connection import ConnectionHandler
+from pslab.instrument.buffer import ADCBufferMixin
+
+
+@pytest.mark.parametrize("starting_position", [0, 1, 10, 200])
+@pytest.mark.parametrize("samples", [3, 128, 129, 260])
+def test_fill_buffer_writes_all_data_at_requested_destination(
+    starting_position, samples
+):
+    buffer = ADCBufferMixin()
+    buffer._device = Mock(spec=ConnectionHandler)
+    data = list(range(samples))
+    buffer.fill_buffer(data, starting_position)
+    expected = []
+    for offset in range(0, samples, 128):
+        values = data[offset : offset + 128]
+        expected += [
+            call.send_byte(CP.COMMON),
+            call.send_byte(CP.FILL_BUFFER),
+            call.send_int(starting_position + offset),
+            call.send_int(len(values)),
+        ]
+        expected += [call.send_int(value) for value in values]
+        expected.append(call.get_ack())
+    assert buffer._device.mock_calls == expected
+    assert data == list(range(samples))
+
+
+def test_fill_buffer_at_zero_keeps_existing_command_sequence():
+    buffer = ADCBufferMixin()
+    buffer._device = Mock(spec=ConnectionHandler)
+    buffer.fill_buffer([7, 8, 9])
+    assert buffer._device.mock_calls == [
+        call.send_byte(CP.COMMON),
+        call.send_byte(CP.FILL_BUFFER),
+        call.send_int(0),
+        call.send_int(3),
+        call.send_int(7),
+        call.send_int(8),
+        call.send_int(9),
+        call.get_ack(),
+    ]
+
+
+def test_fill_buffer_empty_data_does_not_send_commands():
+    buffer = ADCBufferMixin()
+    buffer._device = Mock(spec=ConnectionHandler)
+    buffer.fill_buffer([], starting_position=200)
+    assert buffer._device.mock_calls == []