diff --git a/fdroidserver/metadata.py b/fdroidserver/metadata.py
index 12b8e1e5..1cf5eb96 100644
--- a/fdroidserver/metadata.py
+++ b/fdroidserver/metadata.py
@@ -982,9 +982,12 @@ def write_yaml(mf, app):
         return builds
 
     yaml_app = _app_to_yaml(app)
-    yaml = ruamel.yaml.YAML()
-    yaml.indent(mapping=4, sequence=4, offset=2)
-    yaml.dump(yaml_app, stream=mf)
+    try:
+        yaml = ruamel.yaml.YAML()
+        yaml.indent(mapping=4, sequence=4, offset=2)
+        yaml.dump(yaml_app, stream=mf)
+    except AttributeError:  # Debian/stretch's version does not have YAML()
+        ruamel.yaml.round_trip_dump(yaml_app, mf, indent=4, block_seq_indent=2)
 
 
 build_line_sep = re.compile(r'(?<!\\),')