diff -up src/sage_docbuild/ext/multidocs.py.orig src/sage_docbuild/ext/multidocs.py
--- src/sage_docbuild/ext/multidocs.py.orig	2021-05-09 16:00:11.000000000 -0600
+++ src/sage_docbuild/ext/multidocs.py	2021-05-28 11:32:20.056542939 -0600
@@ -84,8 +84,11 @@ def merge_environment(app, env):
             for ind in newalldoc:
                 # treat subdocument source as orphaned file and don't complain
                 md = env.metadata.get(ind, dict())
-                md['orphan'] = 1
-                env.metadata[ind] = md
+                try:
+                    md['orphan'] = 1
+                    env.metadata[ind] = md
+                except AttributeError:
+                    env.metadata[ind] = {'orphan'}
             # merge the citations
             newcite = {}
             for ind, (path, tag, lineno) in citations.items():
diff -up src/sage/interfaces/singular.py.orig src/sage/interfaces/singular.py
--- src/sage/interfaces/singular.py.orig	2021-05-09 16:00:11.000000000 -0600
+++ src/sage/interfaces/singular.py	2021-05-28 11:29:00.597523201 -0600
@@ -2365,7 +2365,7 @@ def generate_docstring_dictionary():
     nodes.clear()
     node_names.clear()
 
-    singular_docdir = SINGULARPATH + "/../info/"
+    singular_docdir = "/usr/share/info/"
 
     new_node = re.compile(r"File: singular\.hlp,  Node: ([^,]*),.*")
     new_lookup = re.compile(r"\* ([^:]*):*([^.]*)\..*")
@@ -2373,8 +2373,9 @@ def generate_docstring_dictionary():
     L, in_node, curr_node = [], False, None
 
     # singular.hlp contains a few iso-5559-1 encoded special characters
-    with io.open(os.path.join(singular_docdir, 'singular.hlp'),
-                 encoding='latin-1') as f:
+    import gzip
+    with gzip.open(os.path.join(singular_docdir, 'singular.hlp.gz'),
+                   encoding='utf-8') as f:
         for line in f:
             m = re.match(new_node,line)
             if m: