diff --git a/webknossos/webknossos/dataset/downsampling_utils.py b/webknossos/webknossos/dataset/downsampling_utils.py
index b33b74645..c14e31517 100644
--- a/webknossos/webknossos/dataset/downsampling_utils.py
+++ b/webknossos/webknossos/dataset/downsampling_utils.py
@@ -65,12 +65,15 @@ def calculate_mags_to_downsample(
             # The smaller the ratio between the smallest dimension and the largest dimension, the better.
             if all_scaled_ratio < min_scaled_ratio:
                 # Multiply all dimensions with "2"
-                current_mag = Mag(np.minimum(current_mag.to_np() * 2, max_mag.to_np()))
+                new_mag = Mag(np.minimum(current_mag.to_np() * 2, max_mag.to_np()))
             else:
                 # Multiply only the minimal dimension by "2".
-                current_mag = Mag(
-                    np.minimum(current_mag.to_np() * factor, max_mag.to_np())
+                new_mag = Mag(np.minimum(current_mag.to_np() * factor, max_mag.to_np()))
+            if new_mag == current_mag:
+                raise RuntimeError(
+                    f"The maximum mag {max_mag} can not be reached from {current_mag} with scale {scale}!"
                 )
+            current_mag = new_mag
 
         mags += [current_mag]