diff --git a/swugenerator/generator.py b/swugenerator/generator.py
index 628dffe..b19a429 100644
--- a/swugenerator/generator.py
+++ b/swugenerator/generator.py
@@ -201,6 +201,10 @@ def process_entry(self, entry):
                 entry["ivt"] = iv
                 new.ivt = iv
 
+                if "mtdname" in entry or "volume" in entry:
+                    entry.setdefault("properties", {}) \
+                        .update({ "decrypted-size": str(new.getsize()) })
+
             self.artifacts.append(new)
         else:
             logging.debug("Artifact %s already stored", entry["filename"])