diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -38,6 +38,7 @@
     narrowspec,
     node,
     phases,
+    pycompat,
     repository as repositorymod,
     scmutil,
     sshpeer,
@@ -57,7 +58,15 @@
 
 def _local(path):
     path = util.expandpath(util.urllocalpath(path))
-    return (os.path.isfile(path) and bundlerepo or localrepo)
+
+    try:
+        isfile = os.path.isfile(path)
+    # Python 2 raises TypeError, Python 3 ValueError.
+    except (TypeError, ValueError) as e:
+        raise error.Abort(_('invalid path %s: %s') % (
+            path, pycompat.bytestr(e)))
+
+    return isfile and bundlerepo or localrepo
 
 def addbranchrevs(lrepo, other, branches, revs):
     peer = other.peer() # a courtesy to callers using a localrepo for other
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -2051,7 +2051,11 @@
         This is its own function so that extensions can change the definition of
         'valid' in this case (like when pulling from a git repo into a hg
         one)."""
-        return os.path.isdir(os.path.join(path, '.hg'))
+        try:
+            return os.path.isdir(os.path.join(path, '.hg'))
+        # Python 2 may return TypeError. Python 3, ValueError.
+        except (TypeError, ValueError):
+            return False
 
     @property
     def suboptions(self):
diff --git a/tests/test-remotefilelog-gc.t b/tests/test-remotefilelog-gc.t
--- a/tests/test-remotefilelog-gc.t
+++ b/tests/test-remotefilelog-gc.t
@@ -107,6 +107,6 @@
 # Test that warning is displayed when the repo path is malformed
 
   $ printf "asdas\0das" >> $CACHEDIR/repos
-  $ hg gc 2>&1 | head -n2
-  warning: malformed path: * (glob)
-  Traceback (most recent call last):
+  $ hg gc
+  abort: invalid path asdas\x00da: stat() argument 1 must be encoded string without null bytes, not str (esc)
+  [255]