diff --git a/gems/aws-sdk-core/lib/aws-sdk-core/endpoints.rb b/gems/aws-sdk-core/lib/aws-sdk-core/endpoints.rb
index 000eebd1d77..93cd7eca909 100644
--- a/gems/aws-sdk-core/lib/aws-sdk-core/endpoints.rb
+++ b/gems/aws-sdk-core/lib/aws-sdk-core/endpoints.rb
@@ -40,7 +40,7 @@ def resolve_auth_scheme(context, endpoint)
       private
 
       def merge_signing_defaults(auth_scheme, config)
-        if %w[sigv4 sigv4a].include?(auth_scheme['name'])
+        if %w[sigv4 sigv4a sigv4-s3express].include?(auth_scheme['name'])
           auth_scheme['signingName'] ||= sigv4_name(config)
           if auth_scheme['name'] == 'sigv4a'
             # config option supersedes endpoint properties
diff --git a/gems/aws-sdk-core/spec/aws/endpoints_spec.rb b/gems/aws-sdk-core/spec/aws/endpoints_spec.rb
index 7f7750cba6b..5bbaee007f2 100644
--- a/gems/aws-sdk-core/spec/aws/endpoints_spec.rb
+++ b/gems/aws-sdk-core/spec/aws/endpoints_spec.rb
@@ -318,7 +318,7 @@ module Aws
           let(:auth_schemes) { [{ 'name' => 'sigv4-s3express' }] }
 
           it 'defaults the signing region from config' do
-            expect_auth_scheme({ 'signingRegion' => 'us-stubbed-1' })
+            expect_auth({ 'signingRegion' => 'us-stubbed-1' })
             client.operation
           end
         end
diff --git a/gems/aws-sdk-core/spec/sigv4_helper.rb b/gems/aws-sdk-core/spec/sigv4_helper.rb
index 1c01a96f924..62236a6b73a 100644
--- a/gems/aws-sdk-core/spec/sigv4_helper.rb
+++ b/gems/aws-sdk-core/spec/sigv4_helper.rb
@@ -15,7 +15,7 @@ def expect_auth(auth_scheme, region: nil, credentials: nil)
       if auth_scheme['name'] == 'sigv4a'
         mock_signature = Aws::Sigv4::Signature.new(headers: {})
         signer = double('sigv4a_signer', sign_request: mock_signature)
-        region = region_override || args.first['signingRegionSet'].join(',')
+        region = region || args.first['signingRegionSet'].join(',')
 
         expect(Aws::Sigv4::Signer).to receive(:new)
           .with(hash_including(signing_algorithm: :sigv4a, region: region))