diff --git a/roles/matrix-dimension/tasks/validate_config.yml b/roles/matrix-dimension/tasks/validate_config.yml
index f5960142..69971a9b 100644
--- a/roles/matrix-dimension/tasks/validate_config.yml
+++ b/roles/matrix-dimension/tasks/validate_config.yml
@@ -5,3 +5,11 @@
   with_items:
     - "matrix_dimension_access_token"
   when: "matrix_dimension_enabled and vars[item] == ''"
+
+- name: Fail if Matrix Federation is disabled
+  fail:
+    msg: >-
+      You need to enable Matrix Federation to use Dimension. Set `{{ item }}` to 'true'.
+  with_items:
+    - "matrix_synapse_federation_enabled"
+  when: "matrix_dimension_enabled and matrix_synapse_federation_enabled == false"
diff --git a/roles/matrix-dimension/templates/config.yaml.j2 b/roles/matrix-dimension/templates/config.yaml.j2
index 84403d3a..f5f29f4f 100755
--- a/roles/matrix-dimension/templates/config.yaml.j2
+++ b/roles/matrix-dimension/templates/config.yaml.j2
@@ -17,7 +17,7 @@ homeserver:
   # The URL that Dimension should use when trying to communicate with federated APIs on
   # the homeserver. If not supplied or left empty Dimension will try to resolve the address
   # through the normal federation process.
-  federationUrl: "https://matrix-synapse:8448"
+  federationUrl: "http://matrix-synapse:8048"
 
   # The URL that Dimension will redirect media requests to for downloading media such as
   # stickers. If not supplied or left empty Dimension will use the clientServerUrl.