diff --git a/hgext/blackbox.py b/hgext/blackbox.py
--- a/hgext/blackbox.py
+++ b/hgext/blackbox.py
@@ -77,9 +77,13 @@
     class blackboxui(ui.__class__):
         @property
         def _bbvfs(self):
+            vfs = None
             repo = getattr(self, '_bbrepo', None)
             if repo:
-                return repo.vfs
+                vfs = repo.vfs
+                if not vfs.isdir('.'):
+                    vfs = None
+            return vfs
 
         @util.propertycache
         def track(self):
@@ -136,6 +140,10 @@
 
             if not ui:
                 return
+            vfs = ui._bbvfs
+            if not vfs:
+                return
+
             repo = getattr(ui, '_bbrepo', None)
             if not lastui or repo:
                 lastui = ui
diff --git a/tests/test-blackbox.t b/tests/test-blackbox.t
--- a/tests/test-blackbox.t
+++ b/tests/test-blackbox.t
@@ -286,6 +286,14 @@
 
   $ cd ..
 
+With chg, blackbox should not log into other repos
+
+  $ hg init repo1
+  $ hg init repo2
+  $ hg --config extensions.a=! -R repo1 log
+  $ rm -rf $TESTTMP/repo1
+  $ hg --config extensions.a=! init repo1
+
 #endif
 
 blackbox should work if repo.ui.log is not called (issue5518)