diff --git a/lib/email/message_builder.rb b/lib/email/message_builder.rb
index ac3463a5d95..7632a244843 100644
--- a/lib/email/message_builder.rb
+++ b/lib/email/message_builder.rb
@@ -60,8 +60,7 @@ module Email
     def subject
       if @opts[:use_site_subject]
         subject = String.new(SiteSetting.email_subject)
-        subject.gsub!("%{site_name}", @template_args[:site_name])
-        subject.gsub!("%{email_prefix}", @template_args[:email_prefix])
+        subject.gsub!("%{site_name}", @template_args[:email_prefix])
         subject.gsub!("%{optional_re}", @opts[:add_re_to_subject] ? I18n.t('subject_re', @template_args) : '')
         subject.gsub!("%{optional_pm}", @opts[:private_reply] ? I18n.t('subject_pm', @template_args) : '')
         subject.gsub!("%{optional_cat}", @template_args[:show_category_in_subject] ? "[#{@template_args[:show_category_in_subject]}] " : '')
diff --git a/spec/components/email/message_builder_spec.rb b/spec/components/email/message_builder_spec.rb
index 5cf6d4877ac..3ad30558ed0 100644
--- a/spec/components/email/message_builder_spec.rb
+++ b/spec/components/email/message_builder_spec.rb
@@ -199,11 +199,11 @@ describe Email::MessageBuilder do
   context "template_args" do
     let(:template_args) { builder.template_args }
 
-    it "has the email prefix as the site title when `SiteSetting.email_prefix` is not set" do
+    it "has site title as email_prefix when `SiteSetting.email_prefix` is not present" do
       expect(template_args[:email_prefix]).to eq(SiteSetting.title)
     end
 
-    it "has the email prefix as SiteSetting.email_prefix when it is set" do
+    it "has email prefix as email_prefix when `SiteSetting.email_prefix` is present" do
       SiteSetting.email_prefix = 'some email prefix'
       expect(template_args[:email_prefix]).to eq(SiteSetting.email_prefix)
     end
@@ -217,6 +217,19 @@ describe Email::MessageBuilder do
     end
   end
 
+  context "email prefix in subject" do
+    context "when use_site_subject is true" do
+      let(:message_with_email_prefix) { Email::MessageBuilder.new(to_address,
+                                                                  body: 'hello world',
+                                                                  use_site_subject: true) }
+
+      it "when email_prefix is set it should be present in subject" do
+        SiteSetting.email_prefix = 'some email prefix'
+        expect(message_with_email_prefix.subject).to match(SiteSetting.email_prefix)
+      end
+    end
+  end
+
   context "subject_template" do
 
     let(:templated_builder) { Email::MessageBuilder.new(to_address, template: 'mystery') }