diff --git a/NEWS b/NEWS
index 388f8dd7b..6712fdf37 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,6 @@
 ver 0.21.8 (not yet released)
+* output
+  - httpd: add missing mutex lock
 * fix build failure with GCC 9
 
 ver 0.21.7 (2019/04/03)
diff --git a/src/output/plugins/httpd/HttpdClient.cxx b/src/output/plugins/httpd/HttpdClient.cxx
index df4e6ded1..205689462 100644
--- a/src/output/plugins/httpd/HttpdClient.cxx
+++ b/src/output/plugins/httpd/HttpdClient.cxx
@@ -154,7 +154,7 @@ HttpdClient::SendResponse() noexcept
 		FormatWarning(httpd_output_domain,
 			      "failed to write to client: %s",
 			      (const char *)msg);
-		Close();
+		LockClose();
 		return false;
 	}