diff --git a/CHANGES b/CHANGES
index 6ce3e51f3d0..256bb4d6ec1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -67,6 +67,8 @@ Bugs fixed
   at info-field-list
 * #9390: texinfo: Do not emit labels inside footnotes
 * #9979: Error level messages were displayed as warning messages
+* #10057: Failed to scan documents if the project is placed onto the root
+  directory
 
 Testing
 --------
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index 8a3b52fbfca..c773ea05422 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -72,10 +72,9 @@ def get_matching_files(dirname: str,
     """
     # dirname is a normalized absolute path.
     dirname = path.normpath(path.abspath(dirname))
-    dirlen = len(dirname) + 1    # exclude final os.path.sep
 
     for root, dirs, files in os.walk(dirname, followlinks=True):
-        relativeroot = root[dirlen:]
+        relativeroot = path.relpath(root, dirname)
 
         qdirs = enumerate(path_stabilize(path.join(relativeroot, dn))
                           for dn in dirs)  # type: Iterable[Tuple[int, str]]