diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -933,6 +933,8 @@ class Test(unittest.TestCase):
         hgrc.write(b'[largefiles]\n')
         hgrc.write(b'usercache = %s\n' %
                    (os.path.join(self._testtmp, b'.cache/largefiles')))
+        hgrc.write(b'[web]\n')
+        hgrc.write(b'address = localhost\n')
 
         for opt in self._extraconfigopts:
             section, key = opt.split('.', 1)
diff --git a/tests/test-basic.t b/tests/test-basic.t
--- a/tests/test-basic.t
+++ b/tests/test-basic.t
@@ -11,6 +11,7 @@ Create a repository:
   ui.interactive=False
   ui.mergemarkers=detailed
   ui.promptecho=True
+  web.address=localhost
   web.ipv6=True (?)
   $ hg init t
   $ cd t
diff --git a/tests/test-commandserver.t b/tests/test-commandserver.t
--- a/tests/test-commandserver.t
+++ b/tests/test-commandserver.t
@@ -199,6 +199,7 @@ check that local configs for the cached 
   ui.usehttp2=true (?)
   ui.foo=bar
   ui.nontty=true
+  web.address=localhost
   web.ipv6=True (?)
   *** runcommand init foo
   *** runcommand -R foo showconfig ui defaults
diff --git a/tests/test-http-bundle1.t b/tests/test-http-bundle1.t
--- a/tests/test-http-bundle1.t
+++ b/tests/test-http-bundle1.t
@@ -28,11 +28,11 @@ Test server address cannot be reused
 
 #if windows
   $ hg serve -p $HGPORT1 2>&1
-  abort: cannot start server at ':$HGPORT1': * (glob)
+  abort: cannot start server at 'localhost:$HGPORT1': * (glob)
   [255]
 #else
   $ hg serve -p $HGPORT1 2>&1
-  abort: cannot start server at ':$HGPORT1': Address already in use
+  abort: cannot start server at 'localhost:$HGPORT1': Address already in use
   [255]
 #endif
   $ cd ..
diff --git a/tests/test-http.t b/tests/test-http.t
--- a/tests/test-http.t
+++ b/tests/test-http.t
@@ -23,7 +23,7 @@ Test server address cannot be reused
   [255]
 #else
   $ hg serve -p $HGPORT1 2>&1
-  abort: cannot start server at ':$HGPORT1': Address already in use
+  abort: cannot start server at 'localhost:$HGPORT1': Address already in use
   [255]
 #endif
   $ cd ..
diff --git a/tests/test-https.t b/tests/test-https.t
--- a/tests/test-https.t
+++ b/tests/test-https.t
@@ -36,11 +36,11 @@ Test server address cannot be reused
 
 #if windows
   $ hg serve -p $HGPORT --certificate=$PRIV 2>&1
-  abort: cannot start server at ':$HGPORT':
+  abort: cannot start server at 'localhost:$HGPORT':
   [255]
 #else
   $ hg serve -p $HGPORT --certificate=$PRIV 2>&1
-  abort: cannot start server at ':$HGPORT': Address already in use
+  abort: cannot start server at 'localhost:$HGPORT': Address already in use
   [255]
 #endif
   $ cd ..