diff --git a/nixos/doc/manual/release-notes/rl-1709.xml b/nixos/doc/manual/release-notes/rl-1709.xml
index 6948c22cc88f..c16499a0c1d4 100644
--- a/nixos/doc/manual/release-notes/rl-1709.xml
+++ b/nixos/doc/manual/release-notes/rl-1709.xml
@@ -89,6 +89,15 @@ rmdir /var/lib/ipfs/.ipfs
       The <literal>postgres</literal> default <literal>dataDir</literal> has changed from <literal>/var/db/postgres</literal> to <literal>/var/lib/postgresql/$psqlSchema</literal> where $psqlSchema is 9.6 for example.
     </para>
   </listitem>
+  <listitem>
+    <para>
+      The <literal>caddy</literal> service was previously using an extra
+      <literal>.caddy</literal> in the data directory specified with the
+      <literal>dataDir</literal> option. The contents of the
+      <literal>.caddy</literal> directory are now expected to be in the
+      <literal>dataDir</literal>.
+    </para>
+  </listitem>
 </itemizedlist>
 
 
diff --git a/nixos/modules/services/web-servers/caddy.nix b/nixos/modules/services/web-servers/caddy.nix
index 9ac1a08bb586..ee32a1c86d4d 100644
--- a/nixos/modules/services/web-servers/caddy.nix
+++ b/nixos/modules/services/web-servers/caddy.nix
@@ -36,7 +36,11 @@ in
     dataDir = mkOption {
       default = "/var/lib/caddy";
       type = types.path;
-      description = "The data directory, for storing certificates.";
+      description = ''
+        The data directory, for storing certificates. Before 17.09, this
+        would create a .caddy directory. With 17.09 the contents of the
+        .caddy directory are in the specified data directory instead.
+      '';
     };
 
     package = mkOption {
@@ -52,6 +56,8 @@ in
       description = "Caddy web server";
       after = [ "network-online.target" ];
       wantedBy = [ "multi-user.target" ];
+      environment = mkIf (versionAtLeast config.system.stateVersion "17.09")
+        { CADDYPATH = cfg.dataDir; };
       serviceConfig = {
         ExecStart = ''
           ${cfg.package.bin}/bin/caddy -root=/var/tmp -conf=${configFile} \