diff --git a/molyso/mm/channel_detection.py b/molyso/mm/channel_detection.py
index 547f24e..bae0233 100644
--- a/molyso/mm/channel_detection.py
+++ b/molyso/mm/channel_detection.py
@@ -4,6 +4,8 @@
 """
 from __future__ import division, unicode_literals, print_function
 
+import warnings
+
 import numpy as np
 
 from ..debugging import DebugPlot
@@ -397,6 +399,13 @@ def horizontal_mean_frequency(img_frag, clean_around=None, clean_width=0.0):
     # print(collector)
     int_collector = collector.astype(np.int32)
 
+    if (int_collector == 0).all():
+        warnings.warn(
+            "Apparently no channel region was detectable. If the images are flipped, try filename?rotate=<90|270>",
+            RuntimeWarning
+        )
+        return 0, len(int_collector)
+
     bins = np.bincount(int_collector)
     winner = np.argmax(bins[1:]) + 1