diff --git a/batchflow/sampler.py b/batchflow/sampler.py
index cb69843f2..59413d59c 100644
--- a/batchflow/sampler.py
+++ b/batchflow/sampler.py
@@ -235,8 +235,13 @@ def sample(self, size):
 
         up_sample = self.bases[0].sample(size=up_size)
         low_sample  = self.bases[1].sample(size=low_size)
-        sample_points = np.concatenate([up_sample, low_sample])
-        sample_points = sample_points[np.random.permutation(size)]
+        if len(up_sample) > 0 and len(low_sample) > 0:
+            sample_points = np.concatenate([up_sample, low_sample])
+            sample_points = sample_points[np.random.permutation(size)]
+        elif len(up_sample) == 0:
+            sample_points = low_sample
+        else:
+            sample_points = up_sample
 
         return sample_points