diff --git a/pisi/files.py b/pisi/files.py
index 337a858c..1ff92a0c 100644
--- a/pisi/files.py
+++ b/pisi/files.py
@@ -55,7 +55,10 @@ class FileInfo:
         typeElt.appendChild(dom.createTextNode(self.type))
         elt.appendChild(typeElt)
         sizeElt = dom.createElement("Size")
-        sizeElt.appendChild(dom.createTextNode(self.size))
+        size = "0"
+        if self.size:
+            size = self.size
+        sizeElt.appendChild(dom.createTextNode(size))
         elt.appendChild(sizeElt)
         if self.hash:
             hashElt = dom.createElement("SHA1Sum")