diff --git a/.dockerignore b/.dockerignore
index 0b51345cbd..36d243d51f 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -11,6 +11,7 @@
 !Cargo.lock
 !Cargo.toml
 !build_rust.py
+!extra_config.cfg
 
 rust/target
 synapse/*.so