diff --git a/lib/jsonapi/routing_ext.rb b/lib/jsonapi/routing_ext.rb
index b0b94013..6ff8d08f 100644
--- a/lib/jsonapi/routing_ext.rb
+++ b/lib/jsonapi/routing_ext.rb
@@ -48,18 +48,30 @@ def jsonapi_resource(*resources, &_block)
 
           resource @resource_type, options do
             # :nocov:
-            if @scope.respond_to? :[]=
+            if @scope.respond_to?(:[]=)
               # Rails 4
               @scope[:jsonapi_resource] = @resource_type
 
+              if block_given?
+                yield
+              else
+                jsonapi_relationships
+              end
+            elsif Rails::VERSION::MAJOR >= 8 && Rails::VERSION::MINOR >= 1
+              # Rails 8.1+
+              # Rails 8.1 changed Scope to not support []= and Resource.new signature
+              # Use instance variable to track resource type
+              @jsonapi_resource_type = @resource_type
               if block_given?
                 yield
               else
                 jsonapi_relationships
               end
             else
-              # Rails 5
-              jsonapi_resource_scope(SingletonResource.new(@resource_type, api_only?, @scope[:shallow], options), @resource_type) do
+              # Rails 5-8.0
+              resource_arg = SingletonResource.new(@resource_type, api_only?, @scope[:shallow], options)
+
+              jsonapi_resource_scope(resource_arg, @resource_type) do
                 if block_given?
                   yield
                 else
@@ -123,7 +135,7 @@ def jsonapi_resources(*resources, &_block)
 
           resources @resource_type, options do
             # :nocov:
-            if @scope.respond_to? :[]=
+            if @scope.respond_to?(:[]=)
               # Rails 4
               @scope[:jsonapi_resource] = @resource_type
               if block_given?
@@ -131,9 +143,21 @@ def jsonapi_resources(*resources, &_block)
               else
                 jsonapi_relationships
               end
+            elsif Rails::VERSION::MAJOR >= 8 && Rails::VERSION::MINOR >= 1
+              # Rails 8.1+
+              # Rails 8.1 changed Scope to not support []= and Resource.new signature
+              # Use instance variable to track resource type
+              @jsonapi_resource_type = @resource_type
+              if block_given?
+                yield
+              else
+                jsonapi_relationships
+              end
             else
-              # Rails 5
-              jsonapi_resource_scope(Resource.new(@resource_type, api_only?, @scope[:shallow], options), @resource_type) do
+              # Rails 5-8.0
+              resource_arg = Resource.new(@resource_type, api_only?, @scope[:shallow], options)
+
+              jsonapi_resource_scope(resource_arg, @resource_type) do
                 if block_given?
                   yield
                 else
@@ -277,7 +301,7 @@ def jsonapi_resource_scope(resource, resource_type) #:nodoc:
         private
 
         def resource_type_with_module_prefix(resource = nil)
-          resource_name = resource || @scope[:jsonapi_resource]
+          resource_name = resource || @scope[:jsonapi_resource] || @jsonapi_resource_type
           [@scope[:module], resource_name].compact.collect(&:to_s).join('/')
         end
       end
diff --git a/test/integration/requests/request_test.rb b/test/integration/requests/request_test.rb
index a0e7f963..ce55697e 100644
--- a/test/integration/requests/request_test.rb
+++ b/test/integration/requests/request_test.rb
@@ -578,7 +578,8 @@ def test_put_invalid_json
 
     assert_equal 400, status
     assert_equal 'Bad Request', json_response['errors'][0]['title']
-    assert_match 'unexpected token at', json_response['errors'][0]['detail']
+    # Rails 8.1+ has more detailed JSON error messages
+    assert_match(/unexpected token at|expected .* got:|parse error/i, json_response['errors'][0]['detail'])
   end
 
   def test_put_valid_json_but_array
diff --git a/test/test_db-shm b/test/test_db-shm
deleted file mode 100644
index 42eee55d..00000000
Binary files a/test/test_db-shm and /dev/null differ
diff --git a/test/test_db-wal b/test/test_db-wal
deleted file mode 100644
index d750fe47..00000000
Binary files a/test/test_db-wal and /dev/null differ
diff --git a/test/unit/active_relation_resource_finder/join_manager_test.rb b/test/unit/active_relation_resource_finder/join_manager_test.rb
index 840c90ee..19ba1a83 100644
--- a/test/unit/active_relation_resource_finder/join_manager_test.rb
+++ b/test/unit/active_relation_resource_finder/join_manager_test.rb
@@ -6,7 +6,10 @@ class JoinTreeTest < ActiveSupport::TestCase
   def db_true
     case ActiveRecord::Base.connection.adapter_name
       when 'SQLite'
-        if Rails::VERSION::MAJOR >= 6 || (Rails::VERSION::MAJOR >= 5 && ActiveRecord::VERSION::MINOR >= 2)
+        if Rails::VERSION::MAJOR >= 8 && Rails::VERSION::MINOR >= 1
+          # Rails 8.1+ SQLite uses TRUE instead of 1
+          "TRUE"
+        elsif Rails::VERSION::MAJOR >= 6 || (Rails::VERSION::MAJOR >= 5 && ActiveRecord::VERSION::MINOR >= 2)
           "1"
         else
           "'t'"