diff --git a/hosts/sigma/matrix.nix b/hosts/sigma/matrix.nix
index 27dbd1f..9b19313 100644
--- a/hosts/sigma/matrix.nix
+++ b/hosts/sigma/matrix.nix
@@ -1,4 +1,8 @@
-{...}: {
+{
+  config,
+  secrets,
+  ...
+}: {
   # https://element-hq.github.io/synapse/latest/
   # https://nixos.org/manual/nixos/stable/#module-services-matrix
   # https://wiki.nixos.org/wiki/Matrix
@@ -44,6 +48,36 @@
     };
   };
 
+  # https://github.com/matrix-org/sliding-sync
+  services.matrix-synapse.sliding-sync = {
+    # Unlike matrix-synapse, sliding-sync has createDatabase=true by default,
+    # which means we don't have to configure the database in the postgres
+    # service manually.
+    enable = true;
+    settings.SYNCV3_SERVER = config.services.matrix-synapse.settings.public_baseurl;
+    environmentFile = config.age.secrets.matrix-sliding-sync-environment-file.path;
+  };
+
+  services.postgresql = {
+    ensureDatabases = [
+      # matrix-synapse expects the database to have the options `LC_COLLATE`
+      # and `LC_CTYPE` set to `C`, which basically instructs postgres to
+      # ignore any locale-based preferences. Do this manually.
+      # https://github.com/NixOS/nixpkgs/commit/8be61f7a36f403c15e1a242e129be7375aafaa85
+      "matrix-synapse"
+    ];
+    ensureUsers = [
+      # If the database user name equals the connecting system user name,
+      # postgres by default will accept a passwordless connection via unix
+      # domain socket. This makes it possible to run many postgres-backed
+      # services without creating any database secrets at all.
+      {
+        name = "matrix-synapse";
+        ensureDBOwnership = true;
+      }
+    ];
+  };
+
   environment.persistence."/nix/persist" = {
     directories = [
       {
@@ -54,4 +88,11 @@
       }
     ];
   };
+
+  age.secrets.matrix-sliding-sync-environment-file = {
+    file = "${secrets}/secrets/matrix-sliding-sync-environment-file.age";
+    mode = "400";
+    owner = "root";
+    group = "root";
+  };
 }
diff --git a/hosts/sigma/postgresql.nix b/hosts/sigma/postgresql.nix
index 80b4a66..e7a4ae2 100644
--- a/hosts/sigma/postgresql.nix
+++ b/hosts/sigma/postgresql.nix
@@ -6,26 +6,6 @@
     enable = true;
     # https://nixos.org/manual/nixos/stable/#module-services-postgres-upgrading
     package = pkgs.postgresql_16;
-    ensureDatabases = [
-      "matrix-synapse"
-    ];
-    ensureUsers = [
-      # If the database user name equals the connecting system user name,
-      # postgres by default will accept a passwordless connection via unix
-      # domain socket. This makes it possible to run many postgres-backed
-      # services without creating any database secrets at all.
-      {
-        name = "matrix-synapse";
-        ensureDBOwnership = true;
-      }
-    ];
-    initialScript = pkgs.writeText "init.sql" ''
-      # https://github.com/NixOS/nixpkgs/commit/8be61f7a36f403c15e1a242e129be7375aafaa85
-      CREATE DATABASE "matrix-synapse"
-        TEMPLATE template0
-        LC_COLLATE = "C"
-        LC_CTYPE = "C";
-    '';
   };
 
   services.postgresqlBackup = {