diff --git a/cwltool/provenance.py b/cwltool/provenance.py
index 4a88fe67d..30e9d4e8a 100644
--- a/cwltool/provenance.py
+++ b/cwltool/provenance.py
@@ -517,7 +517,7 @@ def guess_mediatype(
             # TODO: Change to nih:sha-256; hashes
             #  https://tools.ietf.org/html/rfc6920#section-7
             aggregate_dict = {
-                "uri": "urn:hash::sha1:" + filename,
+                "uri": "urn:hash:sha1:" + filename,
                 "bundledAs": {
                     # The arcp URI is suitable ORE proxy; local to this Research Object.
                     # (as long as we don't also aggregate it by relative path!)