diff --git a/cypress/integration/vault.spec.js b/cypress/integration/vault.spec.js
--- a/cypress/integration/vault.spec.js
+++ b/cypress/integration/vault.spec.js
@@ -292,7 +292,7 @@
       fixture: `${this.revision.replace(/:/g, '_')}.git.tar`,
       headers: {
         'Content-disposition': `attachment; filename=${this.revision.replace(/:/g, '_')}.git.tar`,
-        'Content-Type': 'application/gzip'
+        'Content-Type': 'application/x-tar'
       }
     }).as('fetchCookedArchive');
 
@@ -506,7 +506,7 @@
       fixture: `${this.revision.replace(/:/g, '_')}.git.tar`,
       headers: {
         'Content-disposition': `attachment; filename=${this.revision.replace(/:/g, '_')}.git.tar`,
-        'Content-Type': 'application/gzip'
+        'Content-Type': 'application/x-tar'
       }
     }).as('fetchCookedArchive');
 
diff --git a/swh/web/api/views/vault.py b/swh/web/api/views/vault.py
--- a/swh/web/api/views/vault.py
+++ b/swh/web/api/views/vault.py
@@ -173,7 +173,7 @@
 
         :param string swhid: the SWHID of the object to cook
 
-        :resheader Content-Type: application/octet-stream
+        :resheader Content-Type: application/gzip
 
         :statuscode 200: no error
         :statuscode 404: requested directory did not receive any cooking
@@ -337,7 +337,7 @@
 
         :param string rev_id: the revision's sha1 identifier
 
-        :resheader Content-Type: application/octet-stream
+        :resheader Content-Type: application/gzip
 
         :statuscode 200: no error
         :statuscode 404: requested directory did not receive any cooking
@@ -474,7 +474,7 @@
 
         :param string swhid: the revision's permanent identifier
 
-        :resheader Content-Type: application/octet-stream
+        :resheader Content-Type: application/x-tar
 
         :statuscode 200: no error
         :statuscode 404: requested directory did not receive any cooking
@@ -489,7 +489,7 @@
         request=request,
     )
     fname = "{}.git.tar".format(swhid)
-    response = HttpResponse(res, content_type="application/gzip")
+    response = HttpResponse(res, content_type="application/x-tar")
     response["Content-disposition"] = "attachment; filename={}".format(
         fname.replace(":", "_")
     )