diff --git a/nixbld-etc-nixos/configuration.nix b/nixbld-etc-nixos/configuration.nix
index a2b9bab..aeac1b4 100644
--- a/nixbld-etc-nixos/configuration.nix
+++ b/nixbld-etc-nixos/configuration.nix
@@ -957,15 +957,10 @@ in
       hydraPath = oa.hydraPath + ":" + super.lib.makeBinPath [ super.jq ];
       doCheck = false;  # FIXME: ldap tests fail on hydra rebuild, seems unrelated to patches above.
     });
-    mattermost = let
-      webapp-new = self.mattermost.webapp.overrideAttrs(oa: {
-      patches = oa.patches or [ ] ++ [ ./mattermost-remove-free-banner.patch ];
-    });
-    in super.mattermost.overrideAttrs(oa: {
-      postInstall = builtins.replaceStrings
-        [ self.mattermost.webapp.outPath ]
-        [ "${webapp-new}" ]
-        oa.postInstall;
+    mattermost = super.mattermost.overrideAttrs(oldAttrs: {
+      webapp = oldAttrs.webapp.overrideAttrs (webappAttrs: {
+        patches = webappAttrs.patches or [ ] ++ [ ./mattermost-remove-free-banner.patch ];
+      });
     });
     matterbridge = super.matterbridge.overrideAttrs(oa: {
       patches = oa.patches or [] ++ [ ./matterbridge-disable-github.patch ];