src/Routing/ReadOnlyModeMethodFilter.php | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/Routing/ReadOnlyModeMethodFilter.php b/src/Routing/ReadOnlyModeMethodFilter.php
index f12920a..b77cb75 100644
--- a/src/Routing/ReadOnlyModeMethodFilter.php
+++ b/src/Routing/ReadOnlyModeMethodFilter.php
@@ -45,6 +45,11 @@ class ReadOnlyModeMethodFilter implements FilterInterface {
    * {@inheritdoc}
    */
   public function filter(RouteCollection $collection, Request $request) {
+    $all_supported_methods = [];
+    foreach ($collection->all() as $name => $route) {
+      $all_supported_methods = array_merge($all_supported_methods, $route->getMethods());
+    }
+
     $collection = $this->inner->filter($collection, $request);
 
     if (!$this->readOnlyModeIsEnabled) {
@@ -52,7 +57,6 @@ class ReadOnlyModeMethodFilter implements FilterInterface {
     }
 
     $read_only_methods = ['GET', 'HEAD', 'OPTIONS', 'TRACE'];
-    $all_supported_methods = [];
     foreach ($collection->all() as $name => $route) {
       if (!$route->hasDefault(Routes::JSON_API_ROUTE_FLAG_KEY)) {
         continue;
@@ -62,14 +66,13 @@ class ReadOnlyModeMethodFilter implements FilterInterface {
       assert(count($supported_methods) > 0, 'JSON:API routes always have a method specified.');
       $is_read_only_route = empty(array_diff($supported_methods, $read_only_methods));
       if (!$is_read_only_route) {
-        $all_supported_methods = array_merge($supported_methods, $all_supported_methods);
         $collection->remove($name);
       }
     }
     if (count($collection)) {
       return $collection;
     }
-    throw new MethodNotAllowedHttpException(array_unique($all_supported_methods), sprintf("JSON:API's read-only mode is enabled. Site administrators can enable writes at %s.", Url::fromRoute('jsonapi.settings')->setAbsolute()->toString(TRUE)->getGeneratedUrl()));
+    throw new MethodNotAllowedHttpException(array_intersect($all_supported_methods, $read_only_methods), sprintf("JSON:API's read-only mode is enabled. Site administrators can enable writes at %s.", Url::fromRoute('jsonapi.settings')->setAbsolute()->toString(TRUE)->getGeneratedUrl()));
   }
 
 }