diff --git a/sync/upstream.py b/sync/upstream.py
index 5be649532..b49f4765c 100644
--- a/sync/upstream.py
+++ b/sync/upstream.py
@@ -629,8 +629,9 @@ def remove_complete_backouts(commits: Iterable[Commit]) -> Sequence[Commit]:
         if commit.is_backout:
             backed_out_commits, _ = commit.wpt_commits_backed_out()
             backed_out = {item.sha1 for item in backed_out_commits}
-            if backed_out.issubset(commits_remaining):
-                commits_remaining -= backed_out
+            intersecion = backed_out.intersection(commits_remaining)
+            if len(intersecion) > 0:
+                commits_remaining -= intersecion
                 continue
         commits_remaining.add(commit.sha1)
 
@@ -686,9 +687,9 @@ def updates_for_backout(git_gecko: Repo,
             sync = syncs.pop()
             assert isinstance(sync, UpstreamSync)
             if commit in sync.gecko_commits:
-                # This commit was already processed
-                backed_out_commit_shas = set()
-                return {}, {}
+                # This commit was already processed for this sync
+                backed_out_commit_shas.remove(backed_out_commit.sha1)
+                continue
             if backed_out_commit in sync.upstreamed_gecko_commits:
                 backed_out_commit_shas.remove(backed_out_commit.sha1)
                 assert sync.bug is not None
diff --git a/test/conftest.py b/test/conftest.py
index 1867ad77b..f658b9968 100644
--- a/test/conftest.py
+++ b/test/conftest.py
@@ -173,7 +173,9 @@ def setup(self):
         self.init()
         with open(os.path.join(self.working_tree, ".hg", "hgrc"), "w") as f:
             f.write("""[ui]
-username=test""")
+username=test
+[extensions]
+shelve=""")
 
     def __getattr__(self, name):
         def call(self, *args):
@@ -349,12 +351,23 @@ def inner(revs, bugs, message=None, bookmarks="mozilla/autoland"):
         if isinstance(bugs, int):
             bugs = [bugs] * len(revs)
         assert len(bugs) == len(revs)
-        msg = [b"Backed out %i changesets (bug %d) for test, r=backout" % (len(revs), bugs[0]), b""]
+        msg = []
+        all_bugs_msgs = []
         for rev, bug in zip(revs, bugs):
             hg_gecko_upstream.backout("--no-commit", rev)
-            msg.append(b"Backed out changeset %s (Bug %d)" % (rev[:12].encode("ascii"), bug))
+            # Shelve the changes so we can perform the next backout.
+            hg_gecko_upstream.shelve()
+            bug_msg = b'bug %d' % bug
+            msg.append(b"Backed out changeset %s (%s)" % (rev[:12].encode("ascii"), bug_msg))
+            all_bugs_msgs.append(bug_msg)
+        bugs_msg = b", ".join(all_bugs_msgs)
+        if len(bugs) > 1:
+            title = [b"Backed out %i changesets (%s) for test, r=backout" % (len(revs), bugs_msg)]
+            msg = title + msg
         if message is None:
             message = b"\n".join(msg)
+        for _ in revs:
+            hg_gecko_upstream.unshelve()
         return hg_commit(hg_gecko_upstream, message, bookmarks)
     return inner
 
diff --git a/test/test_upstream.py b/test/test_upstream.py
index 77ab33ee9..3a3274471 100644
--- a/test/test_upstream.py
+++ b/test/test_upstream.py
@@ -173,6 +173,57 @@ def test_create_partial_backout_reland(git_gecko, git_wpt, upstream_gecko_commit
     sync.wpt_commits[1].metadata["gecko-commit"] == relanding_rev
 
 
+def test_create_backout_of_multiple_bugs(git_gecko, git_wpt, upstream_gecko_commit,
+                                         upstream_gecko_backout):
+    bug = 1234
+    test_changes = {"README": b"Change README\n"}
+    rev = upstream_gecko_commit(test_changes=test_changes, bug=bug,
+                                message=b"Change README")
+
+    update_repositories(git_gecko, git_wpt, wait_gecko_commit=rev)
+    upstream.gecko_push(git_gecko, git_wpt, "autoland", rev,
+                        raise_on_error=True)
+
+    syncs = upstream.UpstreamSync.for_bug(git_gecko, git_wpt, bug)
+
+    bug_2 = 5678
+    test_changes_2 = {"OTHER": b"Add other file\n"}
+    rev_2 = upstream_gecko_commit(test_changes=test_changes_2, bug=bug_2,
+                                  message=b"Add other")
+
+    update_repositories(git_gecko, git_wpt, wait_gecko_commit=rev_2)
+    upstream.gecko_push(git_gecko, git_wpt, "autoland", rev_2,
+                        raise_on_error=True)
+
+    syncs_2 = upstream.UpstreamSync.for_bug(git_gecko, git_wpt, bug_2)
+
+    backout_rev = upstream_gecko_backout([rev_2, rev], [bug_2, bug])
+
+    update_repositories(git_gecko, git_wpt, wait_gecko_commit=backout_rev)
+    upstream.gecko_push(git_gecko, git_wpt, "autoland", backout_rev, raise_on_error=True)
+
+    syncs = upstream.UpstreamSync.for_bug(git_gecko, git_wpt, bug)
+    syncs_2 = upstream.UpstreamSync.for_bug(git_gecko, git_wpt, bug_2)
+
+    assert list(syncs.keys()) == ["incomplete"]
+    assert len(syncs["incomplete"]) == 1
+    sync = syncs["incomplete"].pop()
+    assert sync.status == "incomplete"
+    assert sync.process_name.seq_id == 0
+    assert len(sync.gecko_commits) == 0
+    assert len(sync.upstreamed_gecko_commits) == 1
+    assert len(sync.wpt_commits) == 1
+
+    assert list(syncs_2.keys()) == ["incomplete"]
+    assert len(syncs_2["incomplete"]) == 1
+    sync_2 = syncs_2["incomplete"].pop()
+    assert sync_2.status == "incomplete"
+    assert sync_2.process_name.seq_id == 0
+    assert len(sync_2.gecko_commits) == 0
+    assert len(sync_2.upstreamed_gecko_commits) == 1
+    assert len(sync_2.wpt_commits) == 1
+
+
 def test_land_pr(env, git_gecko, git_wpt, hg_gecko_upstream, upstream_gecko_commit):
     bug = 1234
     test_changes = {"README": b"Change README\n"}