diff --git a/pyleoclim/core/multipleseries.py b/pyleoclim/core/multipleseries.py
index 21c5e7a2..04925cab 100644
--- a/pyleoclim/core/multipleseries.py
+++ b/pyleoclim/core/multipleseries.py
@@ -1057,8 +1057,11 @@ def pca(self,weights=None, name=None, missing='fill-em',tol_em=5e-03, max_em_ite
         '''
         flag, lengths = self.equal_lengths()
 
-        if flag==False:
-            print('All Time Series should be of same length. Apply common_time() first')
+        if flag == False:
+            raise ValueError(
+                "All series must be of the same length to perform PCA; "
+                f"got lengths {lengths}. Apply common_time() first."
+            )
         else: # if all series have equal length
             p = len(lengths)
             n = lengths[0]
diff --git a/pyleoclim/tests/test_core_MultipleSeries.py b/pyleoclim/tests/test_core_MultipleSeries.py
index e319ed29..7f92d135 100644
--- a/pyleoclim/tests/test_core_MultipleSeries.py
+++ b/pyleoclim/tests/test_core_MultipleSeries.py
@@ -313,6 +313,19 @@ def test_pca_t3(self, gen_ts):
         # check that all variance was recovered
         assert abs(res.pctvar.sum() - 100) < 0.001
 
+    def test_pca_t4(self, gen_ts):
+        """
+        Series of unequal length must raise, not return None
+
+        """
+        signal = gen_ts(model="colored_noise", nt=100, alpha=1.0).standardize()
+        long = pyleo.Series(time=np.arange(100), value=signal.value)
+        short = pyleo.Series(time=np.arange(80), value=signal.value[:80])
+        ms = pyleo.MultipleSeries([long, short])
+
+        with pytest.raises(ValueError, match="common_time"):
+            ms.pca()
+
 
 class TestMultipleSeriesIncrements:
     """Test for MultipleSeries.increments()"""