diff --git a/dockerfiles/Synapse.Dockerfile b/dockerfiles/Synapse.Dockerfile
index 0860b9f8..fe86cc5d 100644
--- a/dockerfiles/Synapse.Dockerfile
+++ b/dockerfiles/Synapse.Dockerfile
@@ -24,7 +24,7 @@ COPY keys/* /ca/
 RUN openssl genrsa -out /conf/server.tls.key 2048
 
 # generate a signing key
-RUN generate_signing_key.py -o /conf/server.signing.key
+RUN generate_signing_key -o /conf/server.signing.key
 
 WORKDIR /data