diff --git a/velocyto/analysis.py b/velocyto/analysis.py
index d028f9f..2dd60be 100644
--- a/velocyto/analysis.py
+++ b/velocyto/analysis.py
@@ -1573,7 +1573,9 @@ def default_filter_and_norm(self, min_expr_counts: int=None, min_cells_express:
         if min_cells_express is None:
             min_cells_express = max(10, min(50, self.S.shape[1] * 1.5e-3))
         if N is None:
-            N = max(1000, min(int((self.S.shape[1] / 1000)**(1 / 3) / 0.0008), 5000))
+            N = min(self.S.shape[0], max(1000, min(int((self.S.shape[1] /
+                                                        1000) ** (1 / 3) /
+                                                       0.0008), 5000)))
         if min_avg_U is None:
             min_avg_U = 0.01
         if min_avg_S is None: