diff --git a/src/vorta/utils.py b/src/vorta/utils.py
index fe065b51..4bb37a9b 100644
--- a/src/vorta/utils.py
+++ b/src/vorta/utils.py
@@ -102,7 +102,12 @@ def pretty_bytes(size):
     while size >= power:
         size /= power
         n += 1
-    return f'{round(size, 1)} {Dic_powerN[n]}B'
+    try:
+        unit = Dic_powerN[n]
+        return f'{round(size, 1)} {unit}B'
+    except KeyError as e:
+        logger.error(e)
+        return "NaN"
 
 
 def get_asset(path):