diff --git a/meegkit/dss.py b/meegkit/dss.py
index 0277020e..cc32280a 100644
--- a/meegkit/dss.py
+++ b/meegkit/dss.py
@@ -194,7 +194,7 @@ def dss_line(x, fline, sfreq, nremove=1, nfft=1024, nkeep=None, show=False):
     if nkeep is not None:
         xxx_cov = tscov(xxx)[0]
         V, _ = pca(xxx_cov, nkeep)
-        xxxx = xxx * V
+        xxxx = xxx @ V
     else:
         xxxx = xxx.copy()
 
diff --git a/tests/test_dss.py b/tests/test_dss.py
index ad6e36ec..250e69f7 100644
--- a/tests/test_dss.py
+++ b/tests/test_dss.py
@@ -128,13 +128,15 @@ def test_dss1(show=False):
                     atol=1e-6)  # use abs as DSS component might be flipped
 
 
-def test_dss_line():
+@pytest.mark.parametrize('nkeep', [None, 2])
+def test_dss_line(nkeep):
     """Test line noise removal."""
     sr = 200
+    fline = 20
     nsamples = 10000
     nchans = 10
     x = np.random.randn(nsamples, nchans)
-    artifact = np.sin(np.arange(nsamples) / sr * 2 * np.pi * 20)[:, None]
+    artifact = np.sin(np.arange(nsamples) / sr * 2 * np.pi * fline)[:, None]
     artifact[artifact < 0] = 0
     artifact = artifact ** 3
     s = x + 10 * artifact
@@ -155,24 +157,25 @@ def _plot(x):
         plt.show()
 
     # 2D case, n_outputs == 1
-    out, _ = dss.dss_line(s, 20, sr)
+    out, _ = dss.dss_line(s, fline, sr, nkeep=nkeep)
     _plot(out)
 
     # Test n_outputs > 1
-    out, _ = dss.dss_line(s, 20, sr, nremove=2)
+    out, _ = dss.dss_line(s, fline, sr, nkeep=nkeep, nremove=2)
     # _plot(out)
 
     # Test n_trials > 1
     x = np.random.randn(nsamples, nchans, 4)
-    artifact = np.sin(np.arange(nsamples) / sr * 2 * np.pi * 20)[:, None, None]
+    artifact = np.sin(
+        np.arange(nsamples) / sr * 2 * np.pi * fline)[:, None, None]
     artifact[artifact < 0] = 0
     artifact = artifact ** 3
     s = x + 10 * artifact
-    out, _ = dss.dss_line(s, 20, sr, nremove=1)
+    out, _ = dss.dss_line(s, fline, sr, nremove=1)
 
 
 if __name__ == '__main__':
     pytest.main([__file__])
     # create_data(SNR=5, show=True)
     # test_dss1(True)
-    # test_dss_line()
+    # test_dss_line(None)