diff --git a/sfputil/main.py b/sfputil/main.py
index 1e6416e14c..1e46b90291 100644
--- a/sfputil/main.py
+++ b/sfputil/main.py
@@ -2032,9 +2032,9 @@ def loopback(port_name, loopback_mode, enable):
         sys.exit(EXIT_FAIL)
 
     if 'host-side' in loopback_mode:
-        lane_mask = ((1 << host_lane_count) - 1) << ((subport - 1) * host_lane_count)
+        lane_mask = get_subport_lane_mask(subport, host_lane_count)
     elif 'media-side' in loopback_mode:
-        lane_mask = ((1 << media_lane_count) - 1) << ((subport - 1) * media_lane_count)
+        lane_mask = get_subport_lane_mask(subport, media_lane_count)
     else:
         lane_mask = 0
 
@@ -2055,5 +2055,19 @@ def loopback(port_name, loopback_mode, enable):
         click.echo("{}: Set {} loopback failed".format(port_name, loopback_mode))
         sys.exit(EXIT_FAIL)
 
+
+def get_subport_lane_mask(subport, lane_count):
+    """Get the lane mask for the given subport and lane count
+
+    Args:
+        subport (int): Subport number
+        lane_count (int): Lane count for the subport
+
+    Returns:
+        int: Lane mask for the given subport and lane count
+    """
+    return ((1 << lane_count) - 1) << ((subport - 1) * lane_count)
+
+
 if __name__ == '__main__':
     cli()
diff --git a/tests/sfputil_test.py b/tests/sfputil_test.py
index 5f1374be12..11572efeba 100644
--- a/tests/sfputil_test.py
+++ b/tests/sfputil_test.py
@@ -1709,3 +1709,14 @@ def test_debug_loopback(self, mock_sonic_v2_connector, mock_config_db_connector,
                                ["Ethernet0", "media-side-input", "enable"])
         assert result.output == 'Ethernet0: Failed to connect to STATE_DB\n'
         assert result.exit_code == EXIT_FAIL
+
+    @pytest.mark.parametrize("subport, lane_count, expected_mask", [
+        (1, 1, 0b1),
+        (1, 4, 0b1111),
+        (2, 1, 0b10),
+        (2, 4, 0b11110000),
+        (3, 2, 0b1100),
+        (4, 1, 0b1000),
+    ])
+    def test_get_subport_lane_mask(subport, lane_count, expected_mask):
+        assert get_subport_lane_mask(subport, lane_count) == expected_mask
\ No newline at end of file