diff --git a/mercurial/interfaces/repository.py b/mercurial/interfaces/repository.py
--- a/mercurial/interfaces/repository.py
+++ b/mercurial/interfaces/repository.py
@@ -1027,8 +1027,8 @@
     def get(path, default=None):
         """Obtain the node value for a path or a default value if missing."""
 
-    def flags(path, default=b''):
-        """Return the flags value for a path or a default value if missing."""
+    def flags(path):
+        """Return the flags value for a path (default: empty bytestring)."""
 
     def copy():
         """Return a copy of this manifest."""
diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -460,7 +460,7 @@
     __bool__ = __nonzero__
 
     def __setitem__(self, key, node):
-        self._lm[key] = node, self.flags(key, b'')
+        self._lm[key] = node, self.flags(key)
 
     def __contains__(self, key):
         if key is None:
@@ -595,11 +595,11 @@
         except KeyError:
             return default
 
-    def flags(self, key, default=b''):
+    def flags(self, key):
         try:
             return self._lm[key][1]
         except KeyError:
-            return default
+            return b''
 
     def copy(self):
         c = manifestdict()