diff --git a/drone/fly.toml b/drone/fly.toml
index 25db445..f87eef5 100644
--- a/drone/fly.toml
+++ b/drone/fly.toml
@@ -13,6 +13,7 @@ kill_timeout = 5
   DRONE_JSONNET_ENABLED = "true"
   DRONE_REGISTRATION_CLOSED = "true"
   DRONE_RPC_PROTO = "http"
+  DRONE_RUNNER_CAPACITY = "1"
   DRONE_SERVER_HOST = "build.mat.services"
   DRONE_SERVER_PROTO = "https"