diff --git a/dak/generate_releases.py b/dak/generate_releases.py
index 613c972f6d3aa10e0e005865de9ca73835181a5d..0c106b43028e12c3e23d12d1189347ee2e437f07 100755
--- a/dak/generate_releases.py
+++ b/dak/generate_releases.py
@@ -231,6 +231,16 @@ class ReleaseWriter(object):
                 # probably an uncompressed index we didn't generate
                 continue
 
+            for h in hashes:
+                field = h.release_field
+                hashfile = os.path.join(os.path.dirname(filename), 'by-hash', field, fileinfo[filename][field])
+
+                # if the hash is known to exist, re-use the old file
+                if os.path.exists(hashfile):
+                    os.unlink(filename)
+                    os.link(hashfile, filename)
+                    break
+
             for h in hashes:
                 field = h.release_field
                 hashfile = os.path.join(os.path.dirname(filename), 'by-hash', field, fileinfo[filename][field])