diff --git a/lib/jsonapi/processor.rb b/lib/jsonapi/processor.rb
index 814642a4..a3a9ceb6 100644
--- a/lib/jsonapi/processor.rb
+++ b/lib/jsonapi/processor.rb
@@ -234,16 +234,31 @@ def create_resource
       resource = resource_klass.create(context)
       result = resource.replace_fields(data)
 
-      options = {
-        context: context,
-        fields: fields,
-        filters: { resource_klass._primary_key => resource.id },
-        include_directives: include_directives
-      }
-
-      resource_set = find_resource_set(include_directives, options)
-
-      resource_set.populate!(serializer, context, options)
+      # PORO compatibility: if model doesn't respond to :all, use created resource directly
+      # This restores 0.9.x behavior for PORO models without requiring find_by_key override
+      if resource_klass._model_class.respond_to?(:all)
+        # ActiveRecord path: use find_resource_set for optimized queries with includes
+        options = {
+          context: context,
+          fields: fields,
+          filters: { resource_klass._primary_key => resource.id },
+          include_directives: include_directives
+        }
+
+        resource_set = find_resource_set(include_directives, options)
+        resource_set.populate!(serializer, context, options)
+      else
+        # PORO path: use created resource directly (0.9.x behavior)
+        # ResourceSet will use the resource without calling find
+        resource_set = JSONAPI::ResourceSet.new(resource, include_directives[:include_related], {
+          context: context,
+          fields: fields
+        })
+        resource_set.populate!(serializer, context, {
+          context: context,
+          fields: fields
+        })
+      end
 
       JSONAPI::ResourceSetOperationResult.new((result == :completed ? :created : :accepted), resource_set, result_options)
     end
diff --git a/test/unit/resource/poro_resource_test.rb b/test/unit/resource/poro_resource_test.rb
index 619a99e0..724524b8 100644
--- a/test/unit/resource/poro_resource_test.rb
+++ b/test/unit/resource/poro_resource_test.rb
@@ -11,6 +11,15 @@ def initialize(id, name)
   end
 
   # Note: No .all method - this is a PORO, not ActiveRecord
+
+  # Required for jsonapi-resources compatibility
+  def valid?(_context = nil)
+    true
+  end
+
+  def save(_options = {})
+    true
+  end
 end
 
 # Resource for PORO model
@@ -32,6 +41,22 @@ def create(context)
   end
 end
 
+# PORO Resource without find_by_key override (mimics CallbackTelephoneIncomingResource)
+class MinimalPoroModelResource < JSONAPI::Resource
+  model_name 'PoroModel'
+  attributes :name
+
+  class << self
+    def create(context)
+      model = PoroModel.new(SecureRandom.uuid, "Minimal PORO")
+      new(model, context)
+    end
+
+    # Note: find_by_key is NOT overridden
+    # This should work with the 0.9.x-style create behavior
+  end
+end
+
 class PoroResourceTest < ActiveSupport::TestCase
   def test_poro_model_does_not_respond_to_all
     # Verify our test PORO doesn't have .all method
@@ -98,4 +123,36 @@ def test_active_record_resource_still_uses_original_find_fragments
       assert_kind_of JSONAPI::ResourceFragment, fragment
     end
   end
+
+  def test_create_poro_without_find_by_key_override
+    # This tests the fix for PORO resources that don't override find_by_key
+    # Previously, create would call find_resource_set -> find_fragments -> _model_class.all
+    # which would fail for PORO models without .all method
+    # With the fix, create should return the created resource directly (0.9.x behavior)
+
+    params = {
+      data: {
+        type: 'minimal_poro_models',
+        attributes: {
+          name: 'Test PORO'
+        }
+      },
+      include_directives: JSONAPI::IncludeDirectives.new(MinimalPoroModelResource, []),
+      fields: {},
+      serializer: JSONAPI::ResourceSerializer.new(MinimalPoroModelResource)
+    }
+
+    processor = JSONAPI::Processor.new(MinimalPoroModelResource, :create_resource, params)
+
+    # This should not raise an error (no call to _model_class.all)
+    result = processor.create_resource
+
+    assert_kind_of JSONAPI::ResourceSetOperationResult, result
+    assert result.code == :created || result.code == 201, "Expected :created or 201, got #{result.code.inspect}"
+    assert_not_nil result.resource_set
+
+    # Verify the resource set contains the created resource
+    resources = result.resource_set.instance_variable_get(:@resource_klasses)
+    assert_equal 1, resources[MinimalPoroModelResource].length
+  end
 end