diff --git a/VERSION b/VERSION
index 266146b87cbc8e6d59fe83c426a8500f9549adfb..1dcd3073821d2fc9b4301a966643717a8d14db17 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.6.3
+1.6.4-rc1
diff --git a/arkindex/system_workers.yml b/arkindex/system_workers.yml
index 2867a7a676f2767521a14311484217ef03d08970..c6dd8ae5fefaca4353e02a3c4d7ea08c97a4a073 100644
--- a/arkindex/system_workers.yml
+++ b/arkindex/system_workers.yml
@@ -1,7 +1,7 @@
 # When releasing Arkindex, check that the Docker images set here are up to date,
 # then update the `version` to the current Arkindex version as set in the `VERSION` file
 # to confirm that the images have been manually checked.
-version: 1.6.3
+version: 1.6.4-rc1
 
 features:
     file_import: