diff --git a/api/app/controllers/spree/api/customer_returns_controller.rb b/api/app/controllers/spree/api/customer_returns_controller.rb
index 1e972222274..98d871bfbcc 100644
--- a/api/app/controllers/spree/api/customer_returns_controller.rb
+++ b/api/app/controllers/spree/api/customer_returns_controller.rb
@@ -71,6 +71,10 @@ def build_return_items_from_params
 
         if return_items_params.is_a? ActionController::Parameters
           return_items_params = return_items_params.values
+          Spree::Deprecation.warn(
+            "Passing `return_items_attributes` as a hash of hashes is \
+deprecated and will be removed in future versions of Solidus."
+          )
         end
 
         @customer_return = CustomerReturn.new(customer_return_attributes)
diff --git a/api/spec/requests/spree/api/customer_returns_controller_spec.rb b/api/spec/requests/spree/api/customer_returns_controller_spec.rb
index 6b8bd31b41c..3ec07b1b499 100644
--- a/api/spec/requests/spree/api/customer_returns_controller_spec.rb
+++ b/api/spec/requests/spree/api/customer_returns_controller_spec.rb
@@ -189,6 +189,15 @@ module Spree
             expect(response).to have_http_status(:success)
             expect(json_response).to have_attributes(attributes)
           end
+
+          it "logs a deprecation warning" do
+            expect(Spree::Deprecation).
+              to receive(:warn).
+              with(
+                /Passing `return_items_attributes` as a hash of hashes is deprecated/
+              )
+            subject
+          end
         end
 
         context "with reception_status_event provided for return item" do