diff --git a/lib/spack/external/ruamel/yaml/comments.py b/lib/spack/external/ruamel/yaml/comments.py
index 4a99931615f..b8a5010ad81 100644
--- a/lib/spack/external/ruamel/yaml/comments.py
+++ b/lib/spack/external/ruamel/yaml/comments.py
@@ -381,9 +381,9 @@ def _yaml_get_pre_comment(self):
             pre_comments = self.ca.comment[1] = []
         return pre_comments
 
-    def update(self, vals):
+    def update(self, *vals, **kwds):
         try:
-            ordereddict.update(self, vals)
+            ordereddict.update(self, *vals, **kwds)
         except TypeError:
             # probably a dict that is used
             for x in vals: