diff --git a/nix/modules/hive-gateway.nix b/nix/modules/hive-gateway.nix
index bd461f4f..74af4d26 100644
--- a/nix/modules/hive-gateway.nix
+++ b/nix/modules/hive-gateway.nix
@@ -164,7 +164,29 @@ in
                   "/matrix/" = {
                     alias = "${matrixCfg.gui.package}/";
                     extraConfig = ''
-                      try_files $uri $uri/ /matrix/index.html;
+                      try_files $uri $uri/ @matrix_spa_fallback;
+                    '';
+                  };
+                  # SPA fallback (iris/#643). The naive
+                  # `try_files $uri $uri/ /matrix/index.html;` shape
+                  # silently masked missing static assets — flutter's
+                  # bootstrap requesting e.g. `/matrix/native_executor.js`
+                  # got `index.html` (Content-Type: text/html, status
+                  # 200) when the file was absent from the dist, so
+                  # the JS runtime never loaded and `/matrix/` rendered
+                  # blank without any visible error.
+                  #
+                  # Asset-shaped URIs (anything with a `.<ext>` segment)
+                  # get an explicit 404 so the SPA + browser see the
+                  # missing-asset error cleanly. Only route-shaped URIs
+                  # (no extension) fall through to index.html for SPA
+                  # client-side routing.
+                  "@matrix_spa_fallback" = {
+                    extraConfig = ''
+                      if ($uri ~ "\.[A-Za-z0-9]+$") {
+                        return 404;
+                      }
+                      rewrite ^ /matrix/index.html last;
                     '';
                   };
                 }