diff --git a/pungi/ostree/tree.py b/pungi/ostree/tree.py
index e30d3178..d430a467 100644
--- a/pungi/ostree/tree.py
+++ b/pungi/ostree/tree.py
@@ -101,7 +101,7 @@ class Tree(OSTree):
                 # override ref value in treefile
                 update_dict['ref'] = self.ostree_ref
 
-            tweak_treeconf(self.treefile, source_repos=repos, keep_original_sources=keep_original_sources, update_dict=update_dict)
+            self.treefile = tweak_treeconf(self.treefile, source_repos=repos, keep_original_sources=keep_original_sources, update_dict=update_dict)
 
         self.commitid_file = make_log_file(self.logdir, 'commitid')
 
diff --git a/pungi/ostree/utils.py b/pungi/ostree/utils.py
index 25cb42fb..39d3a379 100644
--- a/pungi/ostree/utils.py
+++ b/pungi/ostree/utils.py
@@ -14,6 +14,7 @@
 # along with this program; if not, see <https://gnu.org/licenses/>.
 
 
+import yaml
 import json
 import logging
 import os
@@ -72,13 +73,20 @@ def tweak_treeconf(treeconf, source_repos=None, keep_original_sources=False, upd
     Additionally, other values can be passed to method by 'update_dict' parameter to
     update treefile content.
     """
-    treeconf_dir = os.path.dirname(treeconf)
-    with open(treeconf, 'r') as f:
-        treeconf_content = json.load(f)
 
     # backup the old tree config
     os.rename(treeconf, '{0}.bak'.format(treeconf))
 
+    treeconf_dir = os.path.dirname(treeconf)
+    with open(treeconf, 'r') as f:
+        # rpm-ostree now supports YAML: https://github.com/projectatomic/rpm-ostree/pull/1377
+        # but we'll end up converting it to JSON.
+        if treeconf.endswith('.yaml'):
+            treeconf_content = yaml.load(f)
+            treeconf = treeconf.replace('.yaml', '.json')
+        else:
+            treeconf_content = json.load(f)
+
     repos = []
     if source_repos:
         # Sort to ensure reliable ordering
@@ -114,3 +122,4 @@ def tweak_treeconf(treeconf, source_repos=None, keep_original_sources=False, upd
     # update tree config to add new repos
     with open(treeconf, 'w') as f:
         json.dump(treeconf_content, f, indent=4)
+    return treeconf