diff --git a/contrib/buildbot/phabricator_wrapper.py b/contrib/buildbot/phabricator_wrapper.py
--- a/contrib/buildbot/phabricator_wrapper.py
+++ b/contrib/buildbot/phabricator_wrapper.py
@@ -389,8 +389,12 @@
         # Use a Diffusion browsequery on the parent directory because the
         # API will fail if a filename is given. If path is not set the root
         # directory is browsed.
+        # Since https://secure.phabricator.com/D21519 the browsequery endpoint
+        # will return an empty result if the trailing slash is missing from the
+        # searched path. There is an exception for the root directory for which
+        # the '/' path is invalid and will throw an error.
         browse_data = self.diffusion.browsequery(
-            path=os.path.dirname(path) or None,
+            path=os.path.join(os.path.dirname(path), '') or None,
             commit=latest_commit_hash,
             repository=BITCOIN_ABC_REPO,
             branch="master",
diff --git a/contrib/buildbot/test/test_phabricator.py b/contrib/buildbot/test/test_phabricator.py
--- a/contrib/buildbot/test/test_phabricator.py
+++ b/contrib/buildbot/test/test_phabricator.py
@@ -261,7 +261,7 @@
     def test_get_file_content_from_master(self):
         commit_hash = "0000000000000000000000000000000123456789"
         file_phid = "PHID-FILE-somefile"
-        path = "some/file"
+        path = "some/file/"
 
         self.phab.get_latest_master_commit_hash = mock.Mock()
         self.phab.get_latest_master_commit_hash.return_value = commit_hash