core/modules/rest/src/Plugin/ResourceBase.php    | 5 ++++-
 core/modules/rest/src/Routing/ResourceRoutes.php | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/core/modules/rest/src/Plugin/ResourceBase.php b/core/modules/rest/src/Plugin/ResourceBase.php
index a3ea800..60d2cdb 100644
--- a/core/modules/rest/src/Plugin/ResourceBase.php
+++ b/core/modules/rest/src/Plugin/ResourceBase.php
@@ -130,7 +130,10 @@ public function routes() {
       // @see \Drupal\rest\RouteProcessor\RestResourceGetRouteProcessorBC
       if ($method === 'GET' || $method === 'HEAD') {
         foreach ($this->serializerFormats as $format_name) {
-          $collection->add("$route_name.$method.$format_name", (new Route(''))->setOption('bc_route', TRUE));
+          $collection->add("$route_name.$method.$format_name", (new Route(''))
+            ->setRequirement('_format', $format_name)
+            ->setOption('bc_route', TRUE)
+          );
         }
       }
     }
diff --git a/core/modules/rest/src/Routing/ResourceRoutes.php b/core/modules/rest/src/Routing/ResourceRoutes.php
index e9d5437..0c616ef 100644
--- a/core/modules/rest/src/Routing/ResourceRoutes.php
+++ b/core/modules/rest/src/Routing/ResourceRoutes.php
@@ -110,6 +110,14 @@ protected function getRoutesForResourceConfig(RestResourceConfigInterface $rest_
           continue;
         }
 
+        // Remove BC routes for unsupported formats.
+        if ($route->getOption('bc_route') === TRUE) {
+          $format_requirement = $route->getRequirement('_format');
+          if ($format_requirement && !in_array($format_requirement, $rest_resource_config->getFormats($method))) {
+            continue;
+          }
+        }
+
         // The configuration has been validated, so we update the route to:
         // - set the allowed response body content types/formats for methods
         //   that may send response bodies