diff --git a/mercurial/keepalive.py b/mercurial/keepalive.py
--- a/mercurial/keepalive.py
+++ b/mercurial/keepalive.py
@@ -90,6 +90,7 @@
 import sys
 import threading
 
+from .i18n import _
 from . import (
     util,
 )
@@ -231,6 +232,10 @@
                 self._cm.add(host, h, 0)
                 self._start_transaction(h, req)
                 r = h.getresponse()
+        # The string form of BadStatusLine is the status line. Add some context
+        # to make the error message slightly more useful.
+        except httplib.BadStatusLine as err:
+            raise urlerr.urlerror(_('bad HTTP status line: %s') % err.line)
         except (socket.error, httplib.HTTPException) as err:
             raise urlerr.urlerror(err)
 
diff --git a/tests/test-http-bad-server.t b/tests/test-http-bad-server.t
--- a/tests/test-http-bad-server.t
+++ b/tests/test-http-bad-server.t
@@ -68,10 +68,8 @@
   $ hg --config badserver.closeafterrecvbytes=1 serve -p $HGPORT -d --pid-file=hg.pid -E error.log
   $ cat hg.pid > $DAEMON_PIDS
 
-TODO this error message is not very good
-
   $ hg clone http://localhost:$HGPORT/ clone
-  abort: error: ''
+  abort: error: bad HTTP status line: ''
   [255]
 
   $ killdaemons.py $DAEMON_PIDS
@@ -87,7 +85,7 @@
   $ hg --config badserver.closeafterrecvbytes=40 serve -p $HGPORT -d --pid-file=hg.pid -E error.log
   $ cat hg.pid > $DAEMON_PIDS
   $ hg clone http://localhost:$HGPORT/ clone
-  abort: error: ''
+  abort: error: bad HTTP status line: ''
   [255]
 
   $ killdaemons.py $DAEMON_PIDS
@@ -104,7 +102,7 @@
   $ hg --config badserver.closeafterrecvbytes=210 serve -p $HGPORT -d --pid-file=hg.pid -E error.log
   $ cat hg.pid > $DAEMON_PIDS
   $ hg clone http://localhost:$HGPORT/ clone
-  abort: error: ''
+  abort: error: bad HTTP status line: ''
   [255]
 
   $ killdaemons.py $DAEMON_PIDS
@@ -143,7 +141,7 @@
   $ cat hg.pid > $DAEMON_PIDS
   $ hg clone http://localhost:$HGPORT/ clone
   requesting all changes
-  abort: error: ''
+  abort: error: bad HTTP status line: ''
   [255]
 
   $ killdaemons.py $DAEMON_PIDS
@@ -200,7 +198,7 @@
   $ cat hg.pid > $DAEMON_PIDS
 
   $ hg clone http://localhost:$HGPORT/ clone
-  abort: error: ''
+  abort: error: bad HTTP status line: ''
   [255]
 
   $ killdaemons.py $DAEMON_PIDS
@@ -251,7 +249,7 @@
   $ cat hg.pid > $DAEMON_PIDS
 
   $ hg clone http://localhost:$HGPORT/ clone
-  abort: error: H
+  abort: error: bad HTTP status line: H
   [255]
 
   $ killdaemons.py $DAEMON_PIDS