diff --git a/hgext3rd/fastlog.py b/hgext3rd/fastlog.py
--- a/hgext3rd/fastlog.py
+++ b/hgext3rd/fastlog.py
@@ -486,8 +486,17 @@
             if self.stopped():
                 break
             self.queue.put((self.id, True, rev))
-
-        self.queue.put((self.id, True, None))
+        # The end marker (self.id, True, None) indicates that the thread
+        # completed successfully. Don't send it if the thread is stopped.
+        # The thread can be stopped for one of two reasons:
+        #  1. The fastlog service failed - in this case, flagging a successful
+        #     finish is harmful, because it will stop us continuing with local
+        #     results, truncating output.
+        #  2. The caller is going to ignore all future results from us. In this
+        #     case, it'll ignore the end marker anyway - it's discarding the
+        #     entire queue.
+        if not self.stopped():
+            self.queue.put((self.id, True, None))
 
 if __name__ == '__main__':
     import doctest
diff --git a/tests/test-fastlog.t b/tests/test-fastlog.t
--- a/tests/test-fastlog.t
+++ b/tests/test-fastlog.t
@@ -250,3 +250,21 @@
   5946a2427fdfcb068a8aec1a59227d0d76062b43
   728676e01661ccc3d7e39de054ca3a7288d7e7b6
 
+Test with failed network call
+  $ cat > $TESTTMP/bad_conduit.py <<'EOF'
+  > def call_conduit(*args, **kwargs):
+  >   raise Exception('failed')
+  > def conduit_config(*args, **kwargs):
+  >   return True
+  > EOF
+
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > fbconduit=$TESTTMP/bad_conduit.py
+  > EOF
+
+  $ hg log parent -T '{rev} {desc}\n' 2>&1 | grep --invert-match 'failed'
+  9 toys
+  8 treats
+  7 cookies
+  6 major repo reorg